lack of recoil-operated semi rifles?... why?


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jason41987
April 17, 2012, 11:20 AM
ive been studying various designs of different firearms.. gaining a better understanding of them, how they function, the physics and engineering behind it all... and well, i seem to find an utter lack of recoil operated rifles... you have the 1941 johnson which wasnt much more than a prototype.. but after that one rifle... nothing

it should be clear that the FAMAS, and HK family rifles are delayed blowback (FAMAS being lever delayed, HK rifles being roller delayed)...

anyway.. blockback rifles have their problems, they usually run on the dirty side, though the simplest of designs, they can be the most dangerous too..

then you have the gas operated family of rifles... long-stroke, short stroke, rotating or tilting bolt, and each of these have their pros and cons as well... long stroke being more reliable, short stroke having less felt recoil.. and well, currently the short-stroke rotating bolt rifles dominate the autoloading market

and then theres the recoil operated design, of which the short-recoil action is in almost every single handgun out there now... long-recoil action was used in the old browning auto 5 shotguns i think..

so besides the johnson rifle which, to my understanding wasnt produced much due to reliability issues with a bayonet attached, and higher cost of production, slower reloading... why hasnt anyone ever went further into the developement of a recoil operated rifle?

advantages would be no gas loss, probably fewer moving parts, some say the '41 johnson had lesser felt recoil, the entire action could be in-line with the barrel and stock, reducing muzzle lift when firing, less weight, not needing a gas tube or piston... so what disadvantages would there be?

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TrickyDick
April 17, 2012, 11:30 AM
I think it may be due to when the bullet is travelling down the barrel, the bolt is moving rearward, thus causing lower accuracy (Equal & Opposite reaction). The idea of gas operated rifles is that the bullet is already exiting the barrel before any parts move. It's not that it won't work, it's just unsuitable for accuracy. this is why recoil operated firearms are usually; pistols, submachineguns and shotguns, where distance/accuracy isn't a huge factor.

jerkface11
April 17, 2012, 11:31 AM
Remington model 8 and 81, for more modern ones there's Highpoint carbines, Kel-tec sub 2000, and the Beretta carbine.

jmr40
April 17, 2012, 11:31 AM
The bolt does not move until after the bullet has left the barrel with any gun design.

Sam1911
April 17, 2012, 11:33 AM
Another recoil-op rifle was the Remington Model 8 (http://en.wikipedia.org/wiki/Remington_Model_8) (later 81).

Several basic issues come to mind. The first, and probably most important, is that when you disconnect the barrel from the action and make it part of the reciprocating mass, accuracy suffers. It HAS to. When you consider how precision rifles focus so heavily on making the barrel and receiver into on solid unit, and stabilizing them against any motion, having the barrel bang back and forth, and then to have locking assemblies with loose enough clearances to be able to disengage and re-engage, and keep working when fouled, there's just no good way around the issue.

(Yes, there were plenty (Auto 5/Rem Model 11, on up the 11-48) and are still a few recoil-operated shotguns (Benellis...sort of). They obviously don't have the precision accuracy concerns to live with.)

Another concern is reliability as you mentioned. Even the shotguns using the recoil action have been known to be temperamental. Gotta be clean. And dry. Or oiled, just right. Or ... who knows? :confused:

And another is that confusingly, recoil-op guns actually tend to produce a stronger recoil sensation than gas-op guns. Strange but true.

briansmithwins
April 17, 2012, 11:37 AM
Recoil operated rifles suffer from the problem that if anything touches the barrel you get a stoppage. You can put a shroud over the barrel but that adds weight.

BSW

animator
April 17, 2012, 11:39 AM
The Barrett M82 is a recoil action with acceptable accuracy.

jmorris
April 17, 2012, 11:42 AM
The first, and probably most important, is that when you disconnect the barrel from the action and make it part of the reciprocating mass, accuracy suffers. It HAS to. .

While I agree with this principal I was shocked to learn my 1919 grouped better at 100 yards that more than a few bolt action rifles I have come across.

68wj
April 17, 2012, 11:45 AM
advantages would be no gas loss, probably fewer moving parts, some say the '41 johnson had lesser felt recoil, the entire action could be in-line with the barrel and stock, reducing muzzle lift when firing, less weight, not needing a gas tube or piston... so what disadvantages would there be?
What does gas loss matter? There isn't enough to cause any effect to the bullet in a gas operated rifle.

Probably fewer moving parts? The old standard M2 .50 cal has many moving parts that have to work in unison together to function. It is more finicky than many believe.

Never shot a Johnson, don't know.

In line with barrel and stock, like a direct impingement AR-15?

Less weight? Part of a recoil operated system is based on the moving masses of its parts. Weight may be increased depending on design.

I am okay with a gas tube or piston, but deleting these parts would be a benefit if someone was opposed to them.

There are modern recoil operated guns though that do work well. Look at the success of Benelli's line of "intertia-driven" guns. However, one of their downsides was discovered when the .mil was looking for a new shotgun in semi-auto form. What happened? Benelli developed a gas piston gun and abandoned its ultra reliable claims of the ID system. This was primarily because of the modular necessities of the military and adding of weight (lights, side saddles, etc) to the gun that affected the recoil mechanism.

Can it be done? SURE. There may not be anything to gain though. Time will tell.

earplug
April 17, 2012, 12:09 PM
Its been about thirty years since I shot a Johnson. I recall the perceived recoil was stronger then a M1/m1A.
Many would agree that a A5 Browning gives more of a kick then a Remington 1100 of the same era.
Accuracy of the recoil operated gun with a moving barrel would be harder to engineer into the design and wear would effect the zero.

jim243
April 17, 2012, 12:15 PM
and well, i seem to find an utter lack of recoil operated rifles...

I really don't understand the question or post. Are you saying that delayed blow back is not a recoil operated rifle??

From the Browning machine gun (M2) to the Thompson Sub-Machine Gun to the Uzi or Mac-10, the MP-5 and of course the Grease Gun of WWII all were and are recoil operated as are all pistols with the exception of the Desert Eagle which is gas operated.

How can you say there has been no development. I believe the M-1 carbine is a recoil design as well (I may be wrong). Just because they do not have a moving barrel does not make them not a recoil operated design (at least in my opinion).

Jim

Oh, yes, I forgot the Remington 74 and 7400

MachIVshooter
April 17, 2012, 12:15 PM
Recoil operated rifles work, but the bottom line is gas operated works better and generally results in a much lighter weapon. The original AR-15 was barely 5 pounds, IIRC. It got heavier to soldier proof it, of course.

Carl N. Brown
April 17, 2012, 12:16 PM
Shooting the Remington 81 in .300 Savage is supposed to be a kick.

You have the momentum of the bolt and barrel recoiling together, and when they stop and seperate, it is supposed to be jolting.

jerkface11
April 17, 2012, 12:17 PM
Shooting the Remington 81 in .300 Savage is supposed to be a kick.

You have the momentum of the bolt and barrel recoiling together, and when they stop and seperate, it is supposed to be jolting.

Mine is a .35 rem and the recoil isn't jolting at all even with a steel buttplate.

rcmodel
April 17, 2012, 12:21 PM
I believe the M-1 carbine is a recoil design as well (I may be wrongShort stroke gas piston.

rc

Tirod
April 17, 2012, 12:26 PM
Recoil operates by causing parts of the weapon to move in the opposite direction of the bullet. Small calibers simply don't offer enough operating mass for reliable actions.

As for those "dirty" blowbacks, consider that what you are really experiencing with any semi auto is "delayed" blowback. Timing has to be advanced enough to get the bolt unlocked as long as the case pressure is low enough to prevent blowing it out. That doesn't mean there isn't any. Gas still blows back past the case onto the action.

Got a piston rifle? Rub a dozen fired cases on your white t-shirt at the range bench and tell me what you get. Fire 40 rounds and then clean the bolt with your t-shirt tail.

Self loading actions all initiate unlocking early enough that the case can be forced against the bolt face. The Army showed in tests with the extractors removed that the M4 will still fire full auto. Under the dynamics of actual operation, extractors slipping off has a lot more to do with bouncing as the bolt is suddenly shocked into reverse - which is why Crane added more spring pressure and an o-ring to counteract it. That stopped the one in a thousand failure to extract, likely caused by a sticking case too swelled from gas pressure to move.

Recoil operated weapons need mass moving to finish the cycle of action, and small calibers don't offer enough. Nonetheless, they get just as dirty as the rest, as those of us who've cleaned the M2 and Mk17 can tell you about.

There's no free lunch there.

Gtscotty
April 17, 2012, 01:01 PM
I really don't understand the question or post. Are you saying that delayed blow back is not a recoil operated rifle??

From the Browning machine gun (M2) to the Thompson Sub-Machine Gun to the Uzi or Mac-10, the MP-5 and of course the Grease Gun of WWII all were and are recoil operated as are all pistols with the exception of the Desert Eagle which is gas operated.

How can you say there has been no development. I believe the M-1 carbine is a recoil design as well (I may be wrong). Just because they do not have a moving barrel does not make them not a recoil operated design (at least in my opinion).


I think you are confusing Blowback/Delayed Blowback actions with Recoil operated actions. I believe recoil operated actions are partially defined by the fact that they are locked during firing. The recoiling barrel/bolt/action/slide, etc, starts moving rearward together upon firing, and at some point in the cycle the action is cammed open to allow for ejection of the spent casing and insertion of a fresh cartridge.

Blowback weapons, on the other hand, fire from an unlocked bolt, only spring tension and the mass of the bolt keep the chamber closed long enough for pressure to drop. For this reason, only relatively low power rounds are generally used in blowback weapons (more powerful rounds would require a much heavier heavier bolt/slide and stronger springs).

Delayed Blowback weapons operate in the same manner as blowback weapons, but incorporate some method of delaying the blowback cycle longer than simple spring weight and bolt mass would. Regardless, it is still just a modified blowback action (as opposed to a recoil operated action), and the bolt is not truely locked during firing.

I'm fairly certain the Rem 74 and 7400 is also gas operated by the way.

I'd agree with pretty much everybody who has answered this post, its harder to achieve top accuracy when most of our action/barrel is moving around with each shot. Also, as some have said, I would not expect a recoil operated rifle to, on average, exhibit the reliability of a similar gas operated rifle.

56hawk
April 17, 2012, 02:00 PM
I'm not sure why there aren't more recoil operated rifles, but I can say it's not because of accuracy. If you look at the longest confirmed sniper kills three of the top ten were with recoil operated rifles. All the others were bolt action.

http://en.wikipedia.org/wiki/Longest_recorded_sniper_kills

BigG
April 17, 2012, 02:22 PM
Weight generally weighs against recoil operation in a shoulder fired rifle. If you look at the operations of a recoil system you know the weight of the operating parts have to equal the recoil of the cartridge less spring which I believe is small. In other words a breech block of a recoil operated 30-06 would be around 7 pounds or so, IIRC. Most people do not want to carry a rifle that weighs more than 7 pounds so the gun would be too heavy. Then there is the moving barrel to deal with... etc.

briansmithwins
April 17, 2012, 06:22 PM
There are only two types of self loading firearm actions: Gas and Recoil.

Blowback and delayed blowback are variants of gas operated: the case is a one use, throw away gas piston.

Recoil actions always involve the barrel moving backwards. Some stay locked for a distance shorter than the case length (short recoil) some stay locked for a distance longer than the case length (long recoil).

There are advantages and disadvantages to both recoil and gas operation. Every design is a compromise.

BSW

Jim Watson
April 17, 2012, 07:40 PM
The shortage of recoil operated rifles is balanced by the plethora of recoil operated handguns.
Gas operation runs the other way.
Like, why is the sky blue and up not down?

Carl N. Brown
April 17, 2012, 09:00 PM
I did overlook that the Barrel M82 .50 rifle is recoil operated: bolt and barrel are locked together, and they recoil locked together for a distance calculated to allow the bullet time to exit the barrel and pressure to drop from its peak, then are un-locked, to allow the bolt to recoil to the rear, with a boost from an accelerator trip (much like the Browning machineguns).

PercyShelley
April 17, 2012, 09:02 PM
I can personally attest that the perceived recoil of a remington 81 in .35 Rem is extremely unpleasant and snappy.

A friend of mine bought one and we took it to the range along with a Swiss Schmidt Rubin m1911 rifle and twenty rounds. We shot about five each and decided it simply wasn't fun. The Schmidt Rubin, 7.5x55 chambering and steel buttplate, was downright tame by comparison.

I suspect what's going on is that the barrel and bolt, which travel quite a ways in this long-recoil design, don't greatly slow down from compressing the recoil and barrel spring and rebound elastically off the receiver. This would make the recoil energy much higher than you would expect for a rifle that heavy. Hatcher's Notebook (http://www.amazon.com/Hatchers-Notebook-Julian-S-Hatcher/dp/0811707954) mentions evidence that something similar happens in 1911 pistols.

jason41987
April 17, 2012, 09:08 PM
yeah.. i dont think accuracy is as much of an issue as believed.. the johnson of WWII and barrett rifles are recoil operated and had better accuracy than many modern battle/assault rifles do now... easily surpassing the poor accuracy of an AK... exactly what the grouping on the johnson was i dont know, never fired one but the claims ive heard that it was pretty close to the garand....

as for recoil.. you can shoulder fire a barrett without just a small fraction of a kick youd get from a bolt action .50bmg... but its well made compensator/brake certainly helps...

i cant seem to find any information on actual accuracy of the 1941 johnson though.. and only on the 1919, but indications are they were still more accurate than a lot of military rifles...

with such limited samples of recoil operated rifles, its hard to say what its limits are.. and if someone made one now, most military carbine rifles arent any longer than the forearm anyway, so a shroud/forearm to cover it wouldnt add much weight

68wj
April 17, 2012, 10:18 PM
yeah.. i dont think accuracy is as much of an issue as believed.. the johnson of WWII and barrett rifles are recoil operated and had better accuracy than many modern battle/assault rifles do now... easily surpassing the poor accuracy of an AK... exactly what the grouping on the johnson was i dont know, never fired one but the claims ive heard that it was pretty close to the garand....

as for recoil.. you can shoulder fire a barrett without just a small fraction of a kick youd get from a bolt action .50bmg... but its well made compensator/brake certainly helps...

i cant seem to find any information on actual accuracy of the 1941 johnson though.. and only on the 1919, but indications are they were still more accurate than a lot of military rifles...

with such limited samples of recoil operated rifles, its hard to say what its limits are.. and if someone made one now, most military carbine rifles arent any longer than the forearm anyway, so a shroud/forearm to cover it wouldnt add much weight
How can you say the Johnson "easily" surpasses the AK when you then say you are unfamiliar with how a Johnson groups (almost a Garand?)? And the Barrett is an apples to oranges comparison when you are talking about a 30 pound, purpose built rifle that IS capable of great accuracy, but gives up the mobility of a service rifle or carbine.

Gtscotty
April 17, 2012, 11:05 PM
And the Barrett is an apples to oranges comparison when you are talking about a 30 pound, purpose built rifle that IS capable of great accuracy, but gives up the mobility of a service rifle or carbine.

It also gives up economy.... at $8-9K a copy, they certainly aren't giving them away. That price level allows for the custom fitting necessary for a recoil operated rifle to achieve the Barrett's excellent level of accuracy. I really don't think you'd be able to build a recoil operated AR-15/AR-10-like rifle with equivalent accuracy for the same price... Having the barrel AND action jump back and forth with each shot is just really not as conducive to accuracy as having the barrel remain in one spot, and the bolt move linearly. I'm not saying it can't be done, its just not the cheapest/most efficient way to go about building an accurate yet reasonably light weight self loading rifle.

Blowback and delayed blowback are variants of gas operated: the case is a one use, throw away gas piston.

.... Correct, in a somewhat esoteric sense, but not really useful. When someone refers to a gas operated action, I think we can safely assume they are generally not referring to a blowback action.

PercyShelley
April 17, 2012, 11:48 PM
Interesting that other posters' experience with the Remington 81 does not mirror my own. I wonder if there is a friction buffer that gets worn out over time. I seem to recall that the auto 5, which is a related design, has something like that.

I have heard, but have not personally verified, that Johnson 1941s are prone to vertical stringing. Whether that's a function of the moving barrel, I would not venture to speculate.

While fussing with a 1911 I noticed something that might limit the scaling on Browning-style tilting barrel short-recoil designs. Because the barrel is tilted out of engagement with the slide while unlocked there is a slight angle between the bore axis and the bolt axis during feeding. This is not a huge issue with stubby pistol rounds (although some have fingered this angle as a potential source of feeding problems in sub-compacts because the angle is larger due to the shorter barrel), but with the long, skinny rifle rounds it seems possible that the round could catch during feeding, or slip from under the extractor.

Most recoil-operated rifles use a separate bolt and bolt carrier, but this would suggest that the most common recoil operated design does not scale up well.

jason41987
April 18, 2012, 08:41 AM
hmm.. ive been thinking about it.. and i wonder... what if there was a recoil operated rifle in which the barrel didnt actually move.. more so like a rear-piston gas system..

imagine this.. the inside of the breach of the barrel is hollowed out.. inside this fits a chamber block that holes and supports the cartridge... when you fire it, this block holding the cartridge slams back, hits a block, forcing the bolt to continue without it, extracting the cartridge... since the breach plug wouldnt completely exit the rear of the barrel, no gasses would escape into the action, they would all be sent forward while the barrel remains still giving the rifle a recoil operation, or an enclosed blowback action, or the breach block could act as a short-stroke piston....

thats one idea ive been working on designing in 3D

jason41987
April 18, 2012, 08:43 AM
hmm.. i can see a problem with fouling in that last idea... might give you the same problems an HK rifle has with buildup in the roller recesses in the barrel

Sam1911
April 18, 2012, 08:53 AM
Have you looked into how the Benelli inertia system works? http://www.benelliusa.com/innovations/

PercyShelley
April 18, 2012, 09:18 AM
jason41987, look up the "floating chamber" .22 adaptors for the 1911. They work similarly to what you describe.

68wj
April 18, 2012, 09:58 AM
jason41987, look up the "floating chamber" .22 adaptors for the 1911. They work similarly to what you describe.
To increase felt recoil.;)

I still don't get the fear of a gas system. Oh noes, gas gets in the action and it is dirty. It is debatable there is any affect on function, and proven that even when stoppages are blamed on fouling, it takes a massive amount of fired rounds to do anything other than make a mess.

Considering cost, accuracy, weight, and reliability, there is currently no better system than gas operated for high power firearms. An autoloader requires an energy source to function, but where does the energy come from? The simple rearward energy (recoil) of a .308 gives ~19-22 ft/lbs while some of that is also absorbed by the shooter and affected by the weight of the firearm. All the while, the action must contain ~60,000 PSI of pressure inside of the chamber. A gas system taps some of that high pressure and uses the energy to cycle the action independent of the shooter's shoulder or weapon's weight. There is the variable of gas pressure for various loads, but a much larger operating window. A 9mm pistol is approximately half the pressure, and a 12ga shotgun even less, so alternate operating systems are more suited here and sometimes ideal.

PercyShelley
April 18, 2012, 10:13 AM
To increase felt recoil.

I still don't get the fear of a gas system. Oh noes, gas gets in the action and it is dirty. It is debatable there is any affect on function, and proven that even when stoppages are blamed on fouling, it takes a massive amount of fired rounds to do anything other than make a mess.

Considering cost, accuracy, weight, and reliability, there is currently no better system than gas operated for high power firearms. An autoloader requires an energy source to function, but where does the energy come from? The simple rearward energy (recoil) of a .308 gives ~19-22 ft/lbs while some of that is also absorbed by the shooter and affected by the weight of the firearm. All the while, the action must contain ~60,000 PSI of pressure inside of the chamber. A gas system taps some of that high pressure and uses the energy to cycle the action independent of the shooter's shoulder or weapon's weight. There is the variable of gas pressure for various loads, but a much larger operating window. A 9mm pistol is approximately half the pressure, and a 12ga shotgun even less, so alternate operating systems are more suited here and sometimes ideal.

More to the point, it increases the recoil velocity of the moving parts, an important consideration if you want to shove around a slide originally dimensioned for a .45 with a mere .22.

I recall a test on arfcom or somesuch were a barrel was chronographed before and after the gas port was drilled. The difference in velocity was slightly above the level of statistical noise (~30 FPS). Most gas systems on semi-auto rifles are designed to bleed gas off after a certain distance. The problem is not finding sufficient energy to cycle the action (excepting weird corner cases like .22 conversions). The problem is managing the enormous amount of energy that there is.

That said, I don't see anything dreadfully wrong with the idea of a recoil-operated rifle. Certainly, it would take a hit in accuracy, but for many applications this wouldn't be enough to matter. A recoil-operated rifle that were only as accurate as, say, an HK USP or custom-tuned 1911 would be more than accurate enough for whacking tasty ungulates at typical distances.

You would shed the mass of the gas system, but you would have to reinforce the receiver where the barrel would be bonking into it. The action is locked, same as a gas-op weapon, so it could handle quite powerful cartridges (as the M82 proves). There would be some sensitivity to using different barrel lengths due to the extra weight, but retarded blowbacks and gas-op rifles usually have to compensate for the longer pressure curve in different length barrels by roller geometry or gas port diameter. So really, it doesn't make an enormous difference which of the three major* self-loading operations cycles a design uses.

The one big advantage I see is that since the barrel is already floating in the receiver, it's fairly easy to remove on most recoil-operated designs. A recoil operated rifle would lend itself well to being a takedown design, and indeed the Remington 81 I've shot could be broken down into two reasonably small halves.


*Now, blow-forward actions, those are just silly.

earplug
April 18, 2012, 10:34 AM
A recoil operated firearm may be very accurate when new. But the barrel sliding and recoiling parts would wear over time. Consider the wear on a match grade pistol.
A fixed barrel design does not have this problem.

jason41987
April 18, 2012, 01:32 PM
seems a floating chamber would give you most most the benefits of a recoil operated design without the negatives which all seem to be present because the barrel itself moves...

this post doesnt neccessarily mean im looking for anything recoil operated, or that it may or may not be a better design... but as this conversation moves on it seems it has roughly the same number of benefits and tradeoffs as any of the other action types (blow back or gas)... which actually doesnt answer any questions... just makes me wonder even more why they, for the most part, just dont exist in rifles... as a student of engineering (i say this not to say im still in school for it, but to emphasize that you'll never stop learning) its in my nature to ask "why" especially when the answers seem to be so elusive

briansmithwins
April 18, 2012, 03:49 PM
seems a floating chamber would give you most most the benefits of a recoil operated design

Floating chambers amplify blowback operation. Useful when doing .22LR conversions but overkill otherwise.

Look up 'primer actuation' for kicks.

If you're a engineering student interested in firearms you need to read The Machine Gun by Col. Chinn. More ideas have been discovered pertaining to firearms than stars in the sky.

http://www.germanmanuals.com/Links.html

BSW

moxie
April 18, 2012, 04:34 PM
Gtscotty is correct. Blowback does not equal recoil operated. the M3 and others mentioned are blowbacks, mostly operating from an open bolt.

SlamFire1
April 18, 2012, 05:17 PM
That said, I don't see anything dreadfully wrong with the idea of a recoil-operated rifle. Certainly, it would take a hit in accuracy, but for many applications this wouldn't be enough to matter. A recoil-operated rifle that were only as accurate as, say, an HK USP or custom-tuned 1911 would be more than accurate enough for whacking tasty ungulates at typical distances.


The basic problem is that it has been so long since these issues where actually hashed out as hardware, no one who was alive then when the downselect occurred, is around now. It is beyond living memory.


LTC Chin's book of the Machine Gun Vol IV goes over the advantages and disadvantages of different mechanisms.


Whatever the theorical advantages of one type over another, what we do know is that gas operation is the most common mechanism for high powered semiautomatic rifles.

And, I don't know exactly why, but it must be because it worked better.

conhntr
April 18, 2012, 05:35 PM
//It also gives up economy.... at $8-9K a copy, they certainly aren't giving them away. That price level allows for the custom fitting necessary for a recoil operated rifle to achieve the Barrett's excellent level of accuracy. I really don't think you'd be able to build a recoil operated AR-15/AR-10-like rifle with equivalent accuracy for the same price//

There is a 1911 manufacturer that can gurantee 50 yard accuracy of 1.5" for 1500$.

briansmithwins
April 18, 2012, 06:31 PM
The big advantage of gas operation is you've got a lot of power to work with and can change the variables a lot. Gas port location, size, and gas piston diameter can all be changed to get the desired result. It's also a lot easier to protect the reciprocating parts (gas piston, operating rod) with some type of shroud than it is to enclose a reciprocating barrel.

BSW

Gtscotty
April 19, 2012, 12:26 AM
There is a 1911 manufacturer that can gurantee 50 yard accuracy of 1.5" for 1500$.

That's interesting, but I'm not sure what a pistol with a mechanical accuracy of 3" at 100 yds has to do with the accuracy of reasonably priced recoil operated rifles. I bet for $1500 you could buy a gas impingement AR pistol that will shoot a group half that size at the same distance. Regardless, I think we are getting into an apples and oranges situation again.

Elkins45
April 20, 2012, 12:29 AM
I have a Marlin Camp Carbine in 9mm and the bolt is a fairly big chunk of steel with a relatively stiff spring. It's a straight blowback design with the barrel rigidly attached to the receiver. AFAIK it's the only blowback centerfire rifle I've ever encountered.

Wonder how heavy the bolt would need to be to build a straight blowback rifle in a powerful centerfire caliber like 30-06? I suspect you would need some serious mass to tame that sort of recoil impulse.

jerkface11
April 20, 2012, 12:53 AM
I can personally attest that the perceived recoil of a remington 81 in .35 Rem is extremely unpleasant and snappy.

That's odd I don't find mine unpleasant at all.

Matthew Courtney
April 20, 2012, 08:21 AM
The bolt does not move until after the bullet has left the barrel with any gun design.
Patently untrue. Most bolt's/breeches stay locked until the bullet leaves the barrel, but most(if not all) of them move the instant the powder is ignited. With recoil operated firearms, the barrel moves with the bolt, which complicates accuracy.

68wj
April 20, 2012, 09:53 AM
Patently untrue. Most bolt's/breeches stay locked until the bullet leaves the barrel, but most(if not all) of them move the instant the powder is ignited. With recoil operated firearms, the barrel moves with the bolt, which complicates accuracy.
In a gas operated weapon, the bolt does not begin to move until after the bullet has passed the gas port and the pressure begins to manipulate the cycling mechanism, relatively long after the powder is ignited. You can also see in many recoil operated firearms how the bolt and barrel remain locked together until a certain point. All of these variables are manipulated through weapon design (timing, tension, mass, etc).

Watch the first few seconds of this pistol here: http://www.youtube.com/watch?v=Rqu9jCuR5P0

jason41987
April 20, 2012, 10:03 AM
i think when you guys talk about accuracy of the recoil operation losing accuracy due to the moving barrel, its not so much the barrel moving before the bullet leaves the barrel, as much as its the likeliness of the barrel not returning to perfect zero every time would be my guess...

unless a chamber could be made to move independant of the barrel... which it could very well be made to do, then it seems like delayed blowback or gas is the way to go for a rifle with a goal of 1 to 1.5MOA in mind

Sam1911
April 20, 2012, 10:37 AM
...its the likeliness of the barrel not returning to perfect zero every time would be my guess...

unless a chamber could be made to move independant of the barrel

Either way, any movement of the barrel or portion of the barrel that is independant of the sighting mechanism, or which has the potential to alter any critical (or even secondary) relationships between the parts of the rifle from shot to shot is the antithesis of the principles of building a precision rifle.

FWIF, the Barrett M82 is not known for being especially accurate, compared to other styles of .50BMG rifle. In fact, Anzio builds a stabilization system to try and help improve things by controlling/limiting barrel movement. All in the attempt to try to bring up the precision of that system to something more like a bolt-action rifle.

jmorris
April 20, 2012, 10:55 AM
The only specimen I have is the 1919 and would say the limit is how far you can haul it.



There is a 1911 manufacturer that can gurantee 50 yard accuracy of 1.5" for 1500$

I have SV's that shoot one hole groups at that distance but at twice the cost. What's the point though, that kind of accuracy is no problem for a 1919 either and more to the point of the thread.



I have a Marlin Camp Carbine in 9mm and the bolt is a fairly big chunk of steel with a relatively stiff spring. It's a straight blowback design with the barrel rigidly attached to the receiver. AFAIK it's the only blowback centerfire rifle I've ever encountered.

There are a lot of centerfire pistol caliber carbines that work the same way, the 9mm AR being a good example, for this thread, as all rifle chamberings use the gas system.

If you wanted a rifle round to work the same you would need to add weight or spring. You would also need to add a hydraulic jack system to rack the bolt if you simply added spring tension.

.45Guy
April 20, 2012, 01:08 PM
Wonder how heavy the bolt would need to be to build a straight blowback rifle in a powerful centerfire caliber like 30-06?
~27 pounds if I recall correctly. (M2 ball)

Really though, everything else aside the reason that recoil operated longarms fell to the wayside is simple economics. I love my 8s and 81s, but I don't foresee anyone bringing such a complex design back into production anytime soon.

briansmithwins
April 20, 2012, 01:10 PM
The bolt does not move until after the bullet has left the barrel with any gun design.

Nope.

On blowback and delayed blowback firearms the bolt starts moving back as soon as the cartridge is ignited. You can get away with this on low pressure, straight walled pistol cartridges, rifle rounds tend to get the case heads torn off because the bolt is opening while the front of the case is still stuck to the chamber walls.

This phenomenon is why HK's delayed blowback weapons have fluted chamber to keep the cases from sticking. The other work around is to oil or grease the cartridges.

BSW

briansmithwins
April 20, 2012, 01:16 PM
On springs:

The spring hardly adds any force to keeping the bolt closed on a blowback operated weapon. Say 9mmP runs at 30k psi. The pressure acting on the head of the case (~0.1^2") is 3000 psi. What spring are you going to use to counteract the 3000 lbs of force that trying to blow the bolt open?

The spring can slow down the bolt (less force acting over a longer travel) and stores the energy needed for cocking, stripping the next cartridge, feeding, and chambering, but it doesn't hold the bolt closed against the force of the cartridge in any design I'm aware of.

BSW

cat9x
April 20, 2012, 01:27 PM
As other's have said there are advantages and disadvantages to recoil operated firearms. The Remington Model 8 & 81 are among the better known long recoil rifles. There were plans once upon a time to scale up the 8/81 action for the 30-06 cartridge but this of course never came to fruition. Felt recoil of 8/81's in 35Rem and 81's in 300Sav are not that bad, but they have more than you would think the round would have. For a video of seeing how the 8/81 platform can be shot, check out the youtube video below,

http://www.youtube.com/watch?v=zILCO-SzVdY

.45Guy
April 20, 2012, 01:41 PM
Great vids!

PercyShelley
April 20, 2012, 01:45 PM
That's odd I don't find mine unpleasant at all.

Yes indeed, I noted the discrepancy. I wonder if the barrel spring was worn on the example I fired, or if there's a friction buffer like in the auto 5 that gets worn out and was in need of replacement.

Obviously, it was some mechanical reason, and not at all possible that I just have daintier shoulders than you do.

~27 pounds if I recall correctly. (M2 ball)


I have lent out my copy of Hatcher's Notebook, but that's about the figure I recall from it for a theoretical straight-blowback .30-06.

Interestingly, straight blowback does scale up very well on cartridges with rebated rims. The Becker family of aircraft cannons (including the type 99 zero-sen wing cannons and the Mk 103 ME-262 nose cannons of WWII fame) are essentially straight blowback. Yes, the firing occurs while the bolt is still moving forwards, but that contributes far less to the reduction of bolt mass than the case head design. I think these used lubricated cartridges.

FWIF, the Barrett M82 is not known for being especially accurate, compared to other styles of .50BMG rifle. In fact, Anzio builds a stabilization system to try and help improve things by controlling/limiting barrel movement.

That is also my understanding. Are M82s even used in competitive shooting alongside bolt action .50s?

I hadn't heard of the Anzio aftermarket tweaks before. That is interesting, thank you.

Sam1911
April 20, 2012, 02:17 PM
I hadn't heard of the Anzio aftermarket tweaks before. That is interesting, thank you.


Looks interesting...

http://www.anzioironworks.com/BARRETT-M82-UPGRADES.htm

Matthew Courtney
April 20, 2012, 04:33 PM
In a gas operated weapon, the bolt does not begin to move until after the bullet has passed the gas port and the pressure begins to manipulate the cycling mechanism, relatively long after the powder is ignited. You can also see in many recoil operated firearms how the bolt and barrel remain locked together until a certain point. All of these variables are manipulated through weapon design (timing, tension, mass, etc).

Watch the first few seconds of this pistol here: http://www.youtube.com/watch?v=Rqu9jCuR5P0
The force of the brass pushing rearward moves the bolt rearward against the locking lug surfaces. If the bolt didn't move back until the lugs mating surfaces were firmly against one another, the lugs would not be needed.

Matthew Courtney
April 20, 2012, 04:38 PM
On springs:

The spring hardly adds any force to keeping the bolt closed on a blowback operated weapon. Say 9mmP runs at 30k psi. The pressure acting on the head of the case (~0.1^2") is 3000 psi. What spring are you going to use to counteract the 3000 lbs of force that trying to blow the bolt open?

The spring can slow down the bolt (less force acting over a longer travel) and stores the energy needed for cocking, stripping the next cartridge, feeding, and chambering, but it doesn't hold the bolt closed against the force of the cartridge in any design I'm aware of.

BSW
3000 psi only equals 3000 pounds of rearward force when the area to which said pressure is applied equals one inch.

68wj
April 20, 2012, 04:50 PM
The force of the brass pushing rearward moves the bolt rearward against the locking lug surfaces. If the bolt didn't move back until the lugs mating surfaces were firmly against one another, the lugs would not be needed.
Yes, force is exerted on the bolt, but that is not moving the bolt outside of any play between the parts. The bolt is not considered a moving part until it begins to unlock.

briansmithwins
April 20, 2012, 06:52 PM
3000 psi only equals 3000 pounds of rearward force when the area to which said pressure is applied equals one inch.

I was using a rough number of 30,000psi for the pressure generated by the burning gas, and I used 1/10th inch for the area. Using those numbers would indeed give a force of 3000psi on the bolt face.

BSW

barnbwt
November 10, 2014, 11:56 PM
Yes, 'tis a necro thread, but this one deserves a resurrection :D

Lots of good info here (mostly towards the end) and a lot of misunderstanding/misinformation. It's mostly semantics, in my opinion, so no need to debate the minutia (yet).

I've found myself thinking about this very question, of late, since recoil operation actually is very common in certain classes of firearms; namely, service pistols, and heavy machine guns. Odd, how wide the gulf is there, isn't it? Granted, the same can be said of blowbacks (weak pocket pistols, SMGs, and the Oerlikon cannon :D) but their appeal is quite plainly their simplicity of function.

I think recoil operation offers a similar simplicity to designers and that's why it was as popular as it was, when it was. We get our cake (powerful chamberings) and the ability to eat it too (both simple and light enough to manufacture and field)

There's two different types of recoil operation; short and long. Short is the only one that actually relies on timing/pressure curves to any extent, and if done wrong, you get case ruptures from early unlocking. Long recoil unlocks veritable eons after pressure has left the barrel, so it's pretty much foolproof in that regard, though typically more mechanically complex. In early machinegun designs, there were both recoil and gas operated schemes, but the latter were almost universally extremely massive (piston/op rods as heavy as the barrel, and nearly as large/long), relegating them to fixed/mounted guns. The Hotchkiss was "portative" not portable. This is because lack of gas-operation knowledge and period technology meant they had to be very aggressively driven, or "over gassed," to function reliably. Everything had to be big to take the needless abuse.

However, recoil operated guns were svelt lightweights operating with miniscule forces by comparison; MG15's, Maxims, Madsens, and later MG34's and 42's for the first true Light Machinegun roles deployable to mobile infantry. The Madsen tagged along in lesser numbers :p. Long stroke, being very safe so long as the locking surfaces are sufficiently strong, came earliest, with later improvements working to decouple the barrel/bolt sooner and sooner --creating the short recoil principle that only has the barrel reciprocate enough to unlock the bolt, and thereby limiting the total moving mass hitting the buffer at the same time.

At least in heavy machine guns, recoil operation is very scalable, from pistols all the way to rifles, to LMGs, HMGs, to large-bore cannons like the KPV in 14.5mm.

Another recurring theme in all these platforms seems to be ease of production for a quality, reliable arm. Recoil operation kicks more, but barrels are neither gas-tapped nor chambers fluted. Receivers are frequently simple tubes with a camming surface cut into them. They may be a bit heavier (since the barrel typically needs to be bushed at the muzzle end, necessitating a long/heavy shroud) but they also require far less cleaning and are far simpler in construction.

After learning that the Johnson/DROR action was basically an AR15 bolt used in short-recoil, I wondered if that might not be the basis for the most simply made of high-powered homebrew firearms;
-Off the shelf AR15 bolt assembly
--The bolt is pinned (by way of the cam pin) into a tubular bolt body that glides in the receiver tube, and is slotted for the hammer (simplified AR BCG)
--The cam pin extends out to form a bolt handle, and carries a roller bearing to act as the camming surface against the receiver (like the Johnson/DROR)
-Off the shelf AR15 barrel of some standard profile
--Simple cylindrical steel/bronze barrel bushings are pressed/threaded onto the gas block (sealing the hole) and barrel-nut seats, and keyed against rotation/over-travel with cross-pins/slots
--Muzzle brakes can either amplify or mitigate recoil as necessary for the configuration used (and a lot more easily than swapping gas systems). Could possibly even be adjustable
-Tubular steel (or possibly aluminum, if galling can be prevented) receiver
--Receiver is slotted on one or both sides for the cam roller track; recoil unlocks bolt after a short distance, and the returning bolt pushes the barrel slightly past its resting place momentarily to cam itself closed (the forward buffer greatly diminishes the stresses on the receiver, possibly allowing the use of aluminum)
--Cam roller slot is oriented/sized so it forms the ejection port (and possibly the magwell on the opposite side if the gun is made left/right swappable)
-Either a simplified sheet metal lower, or setup for buffer-less AR piece

Oddly enough, what I've described is basically a hybrid of the Johnson and the Soviet KPV, but way simpler than either. The layout would basically look like a stretched-out tubular sub-machinegun Now, to go order an AR bolt head and barrel assembly...

TCB

tark
November 12, 2014, 06:16 PM
I have a Remington model 81 in 300 Savage. It shoots two inches at 100 yards with 180 GR ammo. The recoil is not unpleasant, it's just...well....weird.

The gun is a long recoil design so the bolt and barrel recoil together for a full three inches; then the barrel runs itself forward while the bolt stays put. When the barrel stops moving the bolt and bolt carrier are released, to strip another round from the magazine and lock . It is more or less a centerfire version of the A-5 shotgun.

The recoil feels like someone has hit the muzzle of the gun with a baseball bat. It is very sharp and quick, but not all that punishing. Then there is the counter recoil as the whole mass of parts crashes forward again. It feels unlike any other rifle or shotgun I have ever fired.

The problem with the gun, and I think this is to some degree why you don't see more recoil operated guns is this: it is a complicated design and more expensive to manufacture than gas operated designs. My model 81 is a marvelous collection of finely machined and carefully hand fitted parts. But it is an absolute whore's nightmare to try and disassemble. I am quite sure it would not stand up to dirty conditions and / or abuse.

I think you don't see more recoil operated sporting guns out there because gas operation is easier, cheaper, more reliable and overall all around better.

MJ
November 12, 2014, 08:15 PM
Anyone doubt the accuracy of the modern BAR hunting rifle in 7mm MAG?

As what the USMC raiders or early WW2 thought about the Johnson rifle and LMG or the Green Devils of the pre 10th Mountain Div. thought.

Pointless he said she said argument post.

SlamFire1
November 12, 2014, 08:37 PM
It has been a couple of years since I replied to this and I have read up a bit more on mechanisms and the history of machine guns. I have read Chinn’s Vol 1 and several other of his volumes and I think I see a pattern on the evolution of the machine gun. Chinn was interested in big machine guns, not service rifles. What I see in big machine gun evolution is a need for a higher rates of fire. Even during WW1, machine gun cyclic rates had become marginal for air combat, and the most advanced fighter planes of that war were only going about 100 to 120 mph!. As the speed and armor of aircraft increased so did the need for more lead on target in shorter intervals of time.

During the mid 1930’s the 20mm Oerlikon machine cannon, an advanced primer ignition mechanism that required greased cases, became the primary “mid weight” machine gun cannon of the allies. This machine gun was used on basically anything and everything, from Spitfires, landing craft, anti aircraft batteries, you name it. The basic greased round model was used by the Allies, Germans, and Japanese, see chapter 5 http://www.ibiblio.org/hyperwar/USN/ref/MG/I/MG-5.html and it would be interesting to know if any other firearm mechanism was as widely used, by all participants, in WW2.


http://img.photobucket.com/albums/v479/SlamFire/Reloading/Case%20Lubrication/ElcoPTBoatcropped_zps6eaf1786.jpg (http://smg.photobucket.com/user/SlamFire/media/Reloading/Case%20Lubrication/ElcoPTBoatcropped_zps6eaf1786.jpg.html)

This is the Polsten mechanism, no locking lugs, advanced primer ignition, and it required greased rounds or the case would have been ripped apart on extraction.

http://img.photobucket.com/albums/v479/SlamFire/Reloading/Case%20Lubrication/AdvancedPrimerIgnition_zps582455ed.jpg (http://smg.photobucket.com/user/SlamFire/media/Reloading/Case%20Lubrication/AdvancedPrimerIgnition_zps582455ed.jpg.html)

The Hispano was the US Army’s WW2 primary 20 mm machine gun. The mechanism was an advanced primer ignition delayed blowback and required greased rounds to operate. The Oerlikon was a similiar mechanism requiring greased rounds used by the Navy. This table is from Chinn’s Vol III and his book describes the multiple modifications that were made, almost all during WW2, when General Hatcher was in charge of the Ordnance Department.


http://img.photobucket.com/albums/v479/SlamFire/Reloading/Case%20Lubrication/ArmyandNavyGreased20mmcannon2_zps749b3301.jpg (http://smg.photobucket.com/user/SlamFire/media/Reloading/Case%20Lubrication/ArmyandNavyGreased20mmcannon2_zps749b3301.jpg.html)

A primary requirement for both the Army and Navy was 1000 rounds per minute. This is about 17 greased rounds per second. No analysis is provided in Chinn’s book, but it must have dropped out of a lethality analysis based on how many rounds it took to destroy an aircraft going 350 to 400 mph. At those speeds a plane would be in your sights for less than a second and given the ruggedness of the planes, you had to get several hits on target for a reasonable kill probability.

The advantage of an advanced primer ignition mechanism delayed blowback is a high cyclic rate. Take a look at this table that came from AMCP 706-260


http://img.photobucket.com/albums/v479/SlamFire/Reloading/MachineGunfiringrateAMCP706-260.jpg (http://smg.photobucket.com/user/SlamFire/media/Reloading/MachineGunfiringrateAMCP706-260.jpg.html)

A theoretical cyclic rate is being calculated and if you notice, it takes time to unlock, rotate, the bolt. Eliminate those steps and the cyclic rate increases.

By the early 50’s, jets have replaced propeller planes, and even the fastest single barrel reciprocating machine gun can’t shoot fast enough. Multiple barrel, externally powered Gatling type cannons with a cyclic rate around 6000 rounds per minute replace the Oerlikon and Hispano. As air speeds increase even more, explosive warhead missiles replace the Gatling cannons for air combat and most ground air defense systems.

Cyclic rates of 6000 or even 1000 rounds per minute are not needed (though they may be wanted by a ground pounder) in a hand held, man portable weapon. A long recoil mechanism has to travel the full length of the cartridge, but even at rates of 300-500 rpm, a long recoil mechanism would get unwieldy due the weight of the reciprocating mass. My Auto 5 shotgun, a long recoil mechanism, has its own unusual perceived recoil. I can feel the shotgun weight shifting once the barrel is in battery and the bolt moves forward. I believe that something firing a highpower centerfire rifle cartridge with a heavier barrel would really rock and roll under fully automatic fire.

This is what Melvin Johnson says in the Oct 1936 Issue of Army Ordnance about long recoil:


“The worst criticisms of this system are the length of barrel recoil, and the number of tricky parts. The barrel movement requires a “brake” system. Two return springs are necessary. The locking system is complicated and not particularly rugged. Provision for the barrel movement necessitates a tube around the rifle barrel, and this tube retains heat excessively. Of course the movement of the barrel takes care of the unlock and retraction of the breechblock. Using Mark I cartridges, the recoil distance must be increased an undesirable amount, usually over four inches.

Semiautomatic rifles of the long-recoil type have been consistently rejected for military use on the above and other grounds. If the barrel is movable to the extent of more than one-half inch, the weapon will require a complicated receiver or mount, and is quite likely to prove undesirable……”

Melvin Johnson was criticizing all actions types, other than short recoil, so as interesting as this article was about the disadvantages of gas, blowback, delayed blowback, and long recoil mechanisms, it does provide any information disadvantageous to the short recoil mechanism. This should not be a surprise since Melvin Johnson was lobbying to sell the US Army his short recoil rifle! Whatever merits the Johnson rifle might have had, it was doomed never to be adopted, because by the time Melvin Johnson created a suitable working model, the M1 Garand was already in low rate production.

Johnson light machine guns were issued during WW2, but did not last long in service. Don’t know why. I can’t remember an adopted full power short recoil service rifle. It seems to me that the short recoil mechanism would not vibrate excessively, I don’t think it would be as accurate as a fixed barrel gas gun, but service rifles don’t need target accuracy. I am baffled as to what made the short recoil mechanism extinct for high power centerfire rifle cartridges, unless it was a lack of familiarity, or cost.

briansmithwins
November 12, 2014, 08:51 PM
Recoiling barrels in personal weapons suffer from a weight penalty and the problem that touching the barrel on anything will likely result in a stoppage. If you surround the barrel with a shroud (like the recoil operated MG42) you get even more weight.

Rates of fire are influenced the doctrine of the using army. The U.S. Army wanted slow rates of fire (can't be wasting ammo, you know) and they got them, with the M1919, BAR, and M60. The Germans wanted high rates of fire (once you start shooting the enemy goes to ground) and got them with the MG34 and MG42.

The data about the American auto cannons is nice, but neither the Navy or USAAF got a working auto cannon out in time for WWII or Korea.

BSW

SlamFire1
November 12, 2014, 09:15 PM
The data about the American auto cannons is nice, but neither the Navy or USAAF got a working auto cannon out in time for WWII or Korea.

What do you mean by "auto cannon"? Thinking of something else? Chinn says over 150,000 Oerlikon's were made and issued during WW2, and that is just what the Navy bought. They were in service up to the Vietnam war.

Great pictures here:

http://www.ussslater.org/tour/weapons/20mm/20mm.html

barnbwt
November 12, 2014, 09:59 PM
Yay! Folks are still interested in this :cool:

I agree that recoil operation tends to bring with it a weight penalty, but I think the penalty is more from the large reciprocating mass than anything. I would actually agree entirely with Mr. Johnson about long-recoil's inferiority to short recoil, since there really is precious little that is particularly advantageous about the operation for most shoulder-fired weapons.* Long recoil is more complex, mechanically, involves a lot more mass impacting/reciprocating in unison, and I suspect that a muzzle booster is needed to cycle any rifle-length barrel's mass if the cartridge is less powerful than 30-06 (this sort of applies to short recoil, too). That's a lot of downsides, and in areas specifically important for infantry purposes (simplicity, operation that doesn't interrupt sighting, heavier recoil from boosted action). The only upside is you are guaran-darn-teed not to blow the action by unlocking prematurely. Ejection is also more gentle, if the barrel is pulled off the case by a spring instead of it being ripped out at full tilt (which actually was probably a concern for the old-school paper shotgun shells, or brass ones that have always been pricey)

I think a big portion of the reason heavy machine guns tend to be recoil operated is simply because those guns, being mounted, tend to be much more barrel-heavy to preserve barrel life under sustained fire, making that piece sufficiently massive to actuate belt feed mechanisms and large cartridges without additional gas systems being added to the overall weight. If the barrel is too heavy, the addition of a booster cone is an insignificant weight gain. Being mounted, driving all that weight as hard as needed to function has few ramifications for the operator (even a vehicle as light as a technical truck isn't pushed around that much by a KPV)

The important thing about recoil operation, short or long, is recoil velocity; it must be fast enough for the masses involved to cycle the gun. The barrel as a rule is one of/the heaviest parts of the gun. I suspect that fact ends up making the reciprocating/total mass ratio very high. That's bad for infantrymen trying to control the muzzle, but great for mounted guns worried about total mass; I would argue that recoil operation is almost always lighter than a contemporary gas-driven design, with the possible exception of direct impingement, which is likely limited to small-scale weapons.

But, I also think short recoil could circumvent that basic rule about barrel recoil velocity. If the decoupled bolt body was thrown back under mechanical advantage (like a delayed blowback bolt is) the initial recoil velocity of the barrel could be reduced. Combine that with the fact a short recoil design arrests the barrel before the bolt body, and your felt recoil would be greatly diminished, along with the motion jarring the rifle as it cycles. The advantage over a simple delayed blowback would be that the leverage device wouldn't need to be nearly so beefy (it's seeing recoil forces, not bolt thrust), and high pressure cartridges could be safely used without the need for chamber fluting or lubricant coatings. I've actually thought about the possibility of such a 'delayed recoil' operation being used to make a 5.7x28 sub-compact mouse gun, since a normal recoil action that small would be horribly overdriven.

Another way would be to simply cock a spring between the bolt/barrel as they unlock, launching the bolt back as it is freed, and cushioning its return to battery. If the spring-loading could be kept low enough to avoid lug-surface damage, that would seem to make for a very pleasant recoil impulse. It's worth remembering that the decoupled bolt would only need the same momentum as a gas-op bolt+carrier assembly to extract/feed, but could potentially be much lighter/smaller without the carrier attached to it, or the gas system and its weight/recoil.

Lastly, it is worth bringing up the fact that modern infantry rifles use cartridges that allow for narrower, and more importantly shorter barrels. Remember that reaching minimum recoil velocity is the key to a short-recoil gun's operating threshold; our barrels are lighter than ever and very short. That means that peak recoil velocity can be achieved with less recoil impulse (forget boosters and their attendant recoil), and whatever shroud you might think is necessary to shield the barrel (or to mount a launcher/bayonet/accessories on) will shrink as well. Heck, what is a free-float quad rail but an SBR-length barrel shroud, and it looks very likely those will eventually find their way onto our issue rifles in some form.

TCB

*The Gepard GM6 Lynx anti-materiel rifle is long recoil (or at least, very, very long short recoil; I think the bolt actually does unlock before the barrel fully recoils, but not by much). But in that rifle's case, both the massive recoil of heavy cartridges and huge case volume (read: pressure duration) necessitate an operation that is as slow as possible, while still siphoning enough energy/force to extract and strip those big ugly 50BMG rounds assertively. That means lots of slow moving momentum; mass. The heavy barrel damps out the recoil impulse enough to avoid damaging a shooter, and there is no need for additional parts/mass (added to the total) from heavy pistons/gas tubes powerful enough to cycle the gun.

http://25.media.tumblr.com/dfdf8ff0c689c9237f774f0627ccbd87/tumblr_mtyau4w0ln1qk442ao1_500.gif
Just becuz :D

"the problem that touching the barrel on anything will likely result in a stoppage."
Dare you to try inducing a stoppage in the Lynx by grabbing the barrel :neener:. Or an S-18/1000 anti-tank rifle (similar barrel layout, but short recoil operated, and functionally similar to the KPV). I totally agree about smaller stuff, but I personally think the real limiting factor is the loss of the ability to put stuff on the barrel (bayonets, launchers, lights, sights). A free float tube and SBR length barrel would likely overcome those, at least in an infantry gun. I always thought it was funny how the Johnson was derided for poor reliability with a bayonet; I would think the far more serious concern would be how it would function with about 5X the normal "boost" when firing rifle grenades :what: "KABOOM! ...boom (in the distance)" :eek:

Nom de Forum
November 12, 2014, 10:09 PM
Anyone doubt the accuracy of the modern BAR hunting rifle in 7mm MAG?

Reasonably accurate for hunting for a gas operated action.

rcmodel
November 12, 2014, 10:12 PM
The only 7mm Mag BAR I have played with much was an easy 1MOA rifle with a bunch of mixed brand factory loads.

In fact, it was incredibly accurate with certain loads it liked.
And it was very easy on the shoulder.

I liked it, a lot!!!

rc

barnbwt
November 12, 2014, 10:43 PM
...and my 308 FNAR is under an inch at a football field. More accurate than my paltry practice has been able to attain, same as my bolt action 300 SPS.

The BAR/FNAR is piston operated, too, for those folks who'll claim that also makes a gun inaccurate ;)

TCB

Nom de Forum
November 12, 2014, 11:06 PM
The only 7mm Mag BAR I have played with much was an easy 1MOA rifle with a bunch of mixed brand factory loads.

In fact, it was incredibly accurate with certain loads it liked.
And it was very easy on the shoulder.

I liked it, a lot!!!

rc

The point I was attempting to make is that the BAR Hunting Rifle is not a recoil action.

Nom de Forum
November 12, 2014, 11:31 PM
The data about the American auto cannons is nice, but neither the Navy or USAAF got a working auto cannon out in time for WWII or Korea.

BSW

The United States made thousands of copies of the Hispano HS 404 during WWII that had reliability problems. This was primarily due to oversized chambers that eventually were shortened but still not the right size compared to British HS 404s. None the less, except in aircraft were clearing was not possible, they were reliable enough that the U.S.N. abandoned the .50 BMG as fast as possible for the 20mm as the preferred smallest AAA and armed some F6Fs and F4Us with them. Both 20mm and 37mm autocannon were used as armament of American fighter aircraft. The 37mm was also know for reliability problems, a rare thing for a Browning design. By the Korea War the problems with 20mms were corrected. Only the foolishness of some in USAF insisted on .50BMG in fighters until the realities of war changed their minds. The U.S.N. did not suffer from the same foolishness, their Korean era fighters used 20mm cannons.

briansmithwins
November 13, 2014, 04:48 AM
I was referring to auto cannons in U.S. airplanes in WWII, sorry for not making that clear.

As Chinn points out in his book, aircraft weapons need high ROF, extreme reliability, and light weight. 20mm Oerlikon cannons are reliable but not light (400lbs w/200 rounds) and are slow firing (~450 RPM) for aircraft.

BSW

Nom de Forum
November 13, 2014, 01:09 PM
I was referring to auto cannons in U.S. airplanes in WWII, sorry for not making that clear.

As Chinn points out in his book, aircraft weapons need high ROF, extreme reliability, and light weight. 20mm Oerlikon cannons are reliable but not light (400lbs w/200 rounds) and are slow firing (~450 RPM) for aircraft.

BSW


Chinn is right, but you are missing some critical information on actual cannon use in aircraft during WWII that your comment from Chinn is not considering. In WWII six of the eleven American fighter aircraft types used 20mm cannons in at least one their variants. The 37mm cannon was used in the P-39. All of these cannons were manufactured in the United States. The successful engagement range in air to air combat during WWII was nearly always less than 200 yards and often closer. Rates of fire for autocannons as low as the 90 rpm of the M4 37mm were successfully used to engage aircraft because one hit was usually so devastating it resulted in the destruction of a fighter and often a bomber. The Russians appreciated the 37mm so much they armed their Korean War era fighters with at least one 37mm and ended American B-29 missions during daylight. The most numerous autocannon used on American fighters was the American AN/M2 version of the French Hispano HS404 20mm, a combination gas and blowback operated weapon. As a side note, Americans often denigrate the French military, but most who do are probably unaware of the larger number of French military weapons and weapon designs the American military relied upon in both World Wars. The rate of fire of the M2 .50BMG at 600-850 rpm versus the AN/M2 20mm at 600-700 rpm is not significant enough to match the useable terminal ballistic performance of the 20mm. The U.S.N. considered one 20mm to be three times as effective as one .50cal. The 20mm cannon at 112 pounds is only 43% heavier than the .50BMG at 64 pounds. In most fighters the three wing mounted .50s could be replaced by two 20s. Even with a lower quantity of ammunition a 20mm armed fighter has much greater usable destructive power. This really became apparent when computing gunsights available latter in the war. Attempting to hose the sky with many projectiles was shown to be far less effective than short well aimed bursts of fewer projectiles. The major reasons why the 20mm cannon was not the predominant weapon of American aircraft are: shortage of cannons, abundance of M2s and established manufacturing, sloppy American manufacturing of the 20mm resulting in lower reliability, and American military shortsightedness and obstinate resistance to change. If American fighter aircraft during WWII had been required to attack large numbers of heavy bombers similar B-17s and B-24s the famous reputation for destructive power the M2 .50BMG enjoys today would be greatly diminished. Only the ability for the relatively large and strongly built American fighters to carry six to eight .50s with large ammunition supplies against smaller and lighter build adversaries helped to compensate for the lack of 20mm cannons. The most numerous fighter aircraft of WWII, the very effective Bf-109 a.k.a. ME-109, usually was armed with just one 20mm and two MGs. The fact that the armament was fuselage mounted greatly contributed to effectiveness.

sawdeanz
November 13, 2014, 06:04 PM
A related question I am hoping to have answered is why the HK series of arms that are delayed-blowback still have some type of op rod on top?

I'm curious in the main points of the thread too since I love firearm design and learning more about it, and I may look into some of those publications for fun when I have some time.

Nom de Forum
November 13, 2014, 07:10 PM
A related question I am hoping to have answered is why the HK series of arms that are delayed-blowback still have some type of op rod on top?

I'm curious in the main points of the thread too since I love firearm design and learning more about it, and I may look into some of those publications for fun when I have some time.

That is not an op rod. It is the Bolt Head Carrier with Recoil Spring Tube.

barnbwt
November 13, 2014, 08:24 PM
And that, sawdeanz, is the first step towards realizing what a wasteful and inelegant device the ostensibly "perfect" G3/CETME action is. Step two is learning about the need for a self-tensioned bolt head (and the leveraged-cocking handle it requires to open the action), step three the absolute dog's breakfast of a trigger group design. 3.1 would be the pivoting blade ejector, specifically. Fourth would be a selector lever that Jerry Miculek probably has a hard time thumbing (moreso on the CETME). To be honest, the gun was just about as much a piece of work as a design as the M16 ever was, it's just that its issues were more quickly found/solved before it went into action. The one elegant solution in the gun is the way H&K decided to do a forward assist; they put thumb serrations/scallops on the bolt body (can you honestly say the kludge on the side of the AR15 is a better solution for easing the bolt home?)

Oh, it's quite efficient and easy to build...if you have a nation-scale waffenfabrik facility already in place ;)

TCB

PS: Fun fact; a guy going by holescreek converted a G3 to gas operation. IIRC, he replaced the rollers with wedges (so they could not roll and cam back the bolt body) and ran a long-stroke gas piston down the cocking tube housing to a gas block hidden in the front sight triple tree. Worked great, and completely eliminated the need for chamber flutes :cool:. I believe it was in 243, or some other caliber it'd be impossible to get a fluted H&K barrel for :D

Nom de Forum
November 13, 2014, 09:25 PM
[QUOTE]And that, sawdeanz, is the first step towards realizing what a wasteful and inelegant device the ostensibly "perfect" G3/CETME action is. Step two is learning about the need for a self-tensioned bolt head (and the leveraged-cocking handle it requires to open the action), step three the absolute dog's breakfast of a trigger group design. 3.1 would be the pivoting blade ejector, specifically. Fourth would be a selector lever that Jerry Miculek probably has a hard time thumbing (moreso on the CETME). To be honest, the gun was just about as much a piece of work as a design as the M16 ever was, it's just that its issues were more quickly found/solved before it went into action. The one elegant solution in the gun is the way H&K decided to do a forward assist; they put thumb serrations/scallops on the bolt body (can you honestly say the kludge on the side of the AR15 is a better solution for easing the bolt home?)

Oh, it's quite efficient and easy to build...if you have a nation-scale waffenfabrik facility already in place ;)

And that, sawdeanz, is how you end up with "something unstoppable but with no other redeeming qualities" to quote some guy here on THR always going on about such things with such entertainingly blinding brilliance that he could slip in some entertainingly baffling BS and most people would never catch it. BTW the HK91 was the first military style rifle I ever purchased. It is exactly as barnbwt describes.

PS: Fun fact; a guy going by holescreek converted a G3 to gas operation. IIRC, he replaced the rollers with wedges (so they could not roll and cam back the bolt body) and ran a long-stroke gas piston down the cocking tube housing to a gas block hidden in the front sight triple tree. Worked great, and completely eliminated the need for chamber flutes :cool:. I believe it was in 243, or some other caliber it'd be impossible to get a fluted H&K barrel for :D


Didn't I see that one time in a Rube Goldberg cartoon?

Willie Sutton
November 13, 2014, 09:28 PM
"for more modern ones there's Highpoint carbines, Kel-tec sub 2000, and the Beretta carbine"


I note that these are simple blowback designs, not recoil operated designs.

Not a rifle, but the classic Browning shotgun (and Remington Model 11 shotgun) are both long recoil designs as well. Remongton seems to have been the only maonstream maker interested in both rifles and shotguns using this engineering solution.


Willie

.

Nom de Forum
November 13, 2014, 10:15 PM
Hey Willie does that Mig you jockey around still have the 37mm installed?

sawdeanz
November 13, 2014, 10:44 PM
And that, sawdeanz, is the first step towards realizing what a wasteful and inelegant device the ostensibly "perfect" G3/CETME action is. Step two is learning about the need for a self-tensioned bolt head (and the leveraged-cocking handle it requires to open the action), step three the absolute dog's breakfast of a trigger group design. 3.1 would be the pivoting blade ejector, specifically. Fourth would be a selector lever that Jerry Miculek probably has a hard time thumbing (moreso on the CETME). To be honest, the gun was just about as much a piece of work as a design as the M16 ever was, it's just that its issues were more quickly found/solved before it went into action. The one elegant solution in the gun is the way H&K decided to do a forward assist; they put thumb serrations/scallops on the bolt body (can you honestly say the kludge on the side of the AR15 is a better solution for easing the bolt home?)

Oh, it's quite efficient and easy to build...if you have a nation-scale waffenfabrik facility already in place

TCB

PS: Fun fact; a guy going by holescreek converted a G3 to gas operation. IIRC, he replaced the rollers with wedges (so they could not roll and cam back the bolt body) and ran a long-stroke gas piston down the cocking tube housing to a gas block hidden in the front sight triple tree. Worked great, and completely eliminated the need for chamber flutes . I believe it was in 243, or some other caliber it'd be impossible to get a fluted H&K barrel for


Now I'm much more curious about this, didn't realize the design was so complex. You will understand now why I was confused in the first place. Though I always liked the look I could never understand how they could charge so much for a stamped rifle and why if it was so great it needed a fluted chamber. Of course they say its a feature for better reliability but I always figured that was just some bologna they were using to cover up some design handicap. Thanks for confirming my suspicions.

On the other hand G36's seem pretty neat, would like to see those in the states someday.

Nom de Forum
November 13, 2014, 11:54 PM
Now I'm much more curious about this, didn't realize the design was so complex. You will understand now why I was confused in the first place. Though I always liked the look I could never understand how they could charge so much for a stamped rifle and why if it was so great it needed a fluted chamber. Of course they say its a feature for better reliability but I always figured that was just some bologna they were using to cover up some design handicap. Thanks for confirming my suspicions.

On the other hand G36's seem pretty neat, would like to see those in the states someday.

The fluted chamber is not really bologna to cover-up a handicap as it does not create or obscure a limitation on performance. Delay-blowback systems typically do not have mechanical primary extraction so flutes are used to inject gas around the cartridge to "float it" out of the chamber during extraction. This works very well and despite what some people think does not prevent handloaders from reloading the case. Delayed Blowback has been a great operating system for some weapons. An example would be barnbwt's labor of love the Stgw 57 rifle he built, the SIG 510 rifle, SIG 710 GPMG, H&K MP5 SMG, H&K 21 GPMG, and others. Roller Delayed Blowback is not a weakness of the H&K 91/93 rifles. Excessive weight and poor ergonomics are these rifle's primary weaknesses.

barnbwt
November 14, 2014, 12:26 AM
Of course they say its a feature for better reliability but I always figured that was just some bologna they were using to cover up some design handicap
The 'handicap' is the same as if you'd taken an AR15 and been forced to make it run 308 --with no scaling up of components! The rifle is, at its core, really undersized for the power it's handling, so little tricks like the sprung bolt are needed to effectively multiply the force of the recoil spring shutting the action, while also effectively multiplying the bolt weight through mechanical disadvantage at the rollers. Even despite all this leverage slowing things down, the gun still extracts so violently (and so quickly) it will rip cases apart extracting them if they are not 'floated' off the chamber walls on chamber flutes.

Lots of theories about the flutes; the most recent hilarious one I read said the flutes created more surface area for the case to grab onto and thereby increase friction. The flutes are there because the undersized blowback action shifts enough initially while the case is still under pressure and nailed to the chamber walls, that that small shift in bolt face would tear the case body near the head (same as with long headspacing, but not ordinarily as violent due to the initial delay still slowing the process down a lot). By fluting the chamber, the pressure more or less equalizes on the case body, so it isn't glued so forcefully to the walls under pressure. Apparently only the very rear of the case wall area is needed to expand fully to obtain a gas seal, which is why the flutes don't go all the way back (and why the action doesn't vent huge quantities of gas through the flutes).

Even despite all these efforts, enough blowby gets past the flutes, along with whatever residual pressure is left when the case begins moving out of the chamber, that the action gets really nasty, quick.

I like the Swiss approach to delayed blowback better than the German's, because there is no tensioned bolt head. Instead, the bolt tail is about 10X more massive and simply pushes forward against the rollers/bolt head under a strong recoil spring. That, to me, seems like a much more straightforward design solution, though heavier. The heaviness of the srping I do not mind, since it dampens recoil enormously, unlike the G3 which absolutely brutalizes its brass (and flutes have nothing to do with that) since the little bolt carrier is flying around so fast in there (the unique ejection of the STGW helps a lot, too). The STGW is a heavy pig at 14lbs, but it's also built like a true LMG rather than a storm rifle (despite its name in German); long, heavy barrel, giant, heavy stocks, and a bipod. The actual gun between the trunnions isn't notably heavy, especially since the barrel trunnion is so much lighter than the G3. This gun is also shooting a round about the size/power of 30-06, FWIW; a <10lb select fire short barrel variant would be comically impractical (but totally cool)

The cocking system is also way simpler; there's just a non-reciprocating handle on the correct side of the rifle (:p) that rides in a slot, and pulls on the tail of the bolt carrier when yanked on. No super-sensitive, pain-in-the-rear, you'd-better-hope-this-doesn't-break-when-you-need-it lever charging handle with it's weirdo two-part folding/sliding operation. I know full well that H&K's stuff works well once assembled, but getting there is an enormous challenge for anyone outside their factories. A friend completed a CETME while I did my build, and while both were troublesome (that's just sheet metal receivers, for you) his build was far, far more challenging than mine. So long as the bolt drops through the receiver tube, the STGW will very likely work (assuming the barrel is made properly and parts aren't worn down). The CETME requires careful positioning of the pressed-in barrel, cocking tube, and front trunnion --and then you still have to hope your parts aren't worn down when you check your bolt gap. Lord help you if you accidentally let the bolt snap down under that crazy spring when it's out of the gun; dig out the bench vise and cheater bar :D

TCB

Nom de Forum
November 14, 2014, 02:01 AM
The 'handicap' is the same as if you'd taken an AR15 and been forced to make it run 308 --with no scaling up of components! The rifle is, at its core, really undersized for the power it's handling, so little tricks like the sprung bolt are needed to effectively multiply the force of the recoil spring shutting the action, while also effectively multiplying the bolt weight through mechanical disadvantage at the rollers. Even despite all this leverage slowing things down, the gun still extracts so violently (and so quickly) it will rip cases apart extracting them if they are not 'floated' off the chamber walls on chamber flutes.

Lots of theories about the flutes; the most recent hilarious one I read said the flutes created more surface area for the case to grab onto and thereby increase friction. The flutes are there because the undersized blowback action shifts enough initially while the case is still under pressure and nailed to the chamber walls, that that small shift in bolt face would tear the case body near the head (same as with long headspacing, but not ordinarily as violent due to the initial delay still slowing the process down a lot). By fluting the chamber, the pressure more or less equalizes on the case body, so it isn't glued so forcefully to the walls under pressure. Apparently only the very rear of the case wall area is needed to expand fully to obtain a gas seal, which is why the flutes don't go all the way back (and why the action doesn't vent huge quantities of gas through the flutes).

Even despite all these efforts, enough blowby gets past the flutes, along with whatever residual pressure is left when the case begins moving out of the chamber, that the action gets really nasty, quick.

I like the Swiss approach to delayed blowback better than the German's, because there is no tensioned bolt head. Instead, the bolt tail is about 10X more massive and simply pushes forward against the rollers/bolt head under a strong recoil spring. That, to me, seems like a much more straightforward design solution, though heavier. The heaviness of the srping I do not mind, since it dampens recoil enormously, unlike the G3 which absolutely brutalizes its brass (and flutes have nothing to do with that) since the little bolt carrier is flying around so fast in there (the unique ejection of the STGW helps a lot, too). The STGW is a heavy pig at 14lbs, but it's also built like a true LMG rather than a storm rifle (despite its name in German); long, heavy barrel, giant, heavy stocks, and a bipod. The actual gun between the trunnions isn't notably heavy, especially since the barrel trunnion is so much lighter than the G3. This gun is also shooting a round about the size/power of 30-06, FWIW; a <10lb select fire short barrel variant would be comically impractical (but totally cool)

The cocking system is also way simpler; there's just a non-reciprocating handle on the correct side of the rifle (:p) that rides in a slot, and pulls on the tail of the bolt carrier when yanked on. No super-sensitive, pain-in-the-rear, you'd-better-hope-this-doesn't-break-when-you-need-it lever charging handle with it's weirdo two-part folding/sliding operation. I know full well that H&K's stuff works well once assembled, but getting there is an enormous challenge for anyone outside their factories. A friend completed a CETME while I did my build, and while both were troublesome (that's just sheet metal receivers, for you) his build was far, far more challenging than mine. So long as the bolt drops through the receiver tube, the STGW will very likely work (assuming the barrel is made properly and parts aren't worn down). The CETME requires careful positioning of the pressed-in barrel, cocking tube, and front trunnion --and then you still have to hope your parts aren't worn down when you check your bolt gap. Lord help you if you accidentally let the bolt snap down under that crazy spring when it's out of the gun; dig out the bench vise and cheater bar :D

TCB


By your own admission the Stgw 57 is a pig at 14lbs. That pig is not much of a burden for Swiss soldiers who intended to use almost static defense tactics against invaders attempting to negotiate mountain passes. The H&K 91 a.k.a. Bundswehr G3 rifle’s “little tricks” make it 40% lighter enabling it to be much better suited to defending the plains of Northern Germany. The flutes do an excellent job “floating” the cases off the chamber walls. I have never seen a H&K rip-off a case head. The ejection is forceful, cases are dented by the ejection port, but in some situations excess ejection power is a good thing. Sure the receiver gets gunky from firing but it is no more serious problem than it is for a MAS 49 or M16, both known for getting gunky and still operating. I think H&K did a good job making the rifle design shoot a more powerful cartridge than it was originally intended to shoot. I agree the Swiss SIG is more elegant in design but it is very expensive and heavy. Long barrels in HKs seem to work fine in the PSG sniper version of the G3. I don’t know about heavy bullet working in an HK other than some cast lead 169gr reloads I shot in mine that all went bang and ejected. I do think the H&K design could handle the power of 7.5 Swiss Ball because if you do some checking you will find in military loadings it is nearly identical in power to 7.62 Nato M80 Ball and .30-06 M1 and M2 Ball.

Lord help you if you accidentally let the bolt snap down under that crazy spring when it's out of the gun; dig out the bench vise and cheater bar.

Naw, you don't need to worry about that or use a bench vise and cheater bar. Insert the Bolt Head Carrier backwards into the receiver until it stops. Smack the Bolt Head Carrier Recoil Spring Tube with the palm of your hand. The Bolt rollers will pop back in when the bolt moves. Remove the backwards Bolt Head Carrier then reassemble the rifle. That is the easy way. The harder way is to use strong hands to just pull the bolt head to pop the rollers in. I used to do that when I was younger and stronger.

barnbwt
November 14, 2014, 02:51 AM
"I have never seen a H&K rip-off a case head."
Shoot one without flutes, sometime ;). They really are quite necessary for function; it's not a 'reliability enhancement' at all. The ripping/tearing is most commonly seen in Century hack-jobs that are marginal at best in bolt gap, but it's happened with stuck cases, too (or at the least the case rim is ripped out). Strong ejection is nice, but ridiculous ejection is ridiculous; some of those G3's are straight up hazardous to anyone nearby (I've seen cases stuck into boards, before :eek:)

"I think H&K did a good job making the rifle design shoot a more powerful cartridge than it was originally intended to shoot."
Abso-tively. I honestly would love to have been a fly on the wall at CETME Engineering when the decision to go to 308 was made. I suspect there was a stony silence, then engineers one after another wondering how the heck they were gonna pull this off :p

Totally agree on the STGW being heavy. I think the best solution would have been if H&K could have adopted SIG's trunnion design (with replaceable recesses and like 1/3rd the weight of the CETME part) but adapted it to work with their simpler sheet metal form. The SIG bolt really isn't all that much heavier; the trunnion weight savings probably make up for it, in fact. With a simpler bolt setup, the modified H&K could have a basic non-folding charging handle with the original layout of a spring over the barrel, or a buffer tube inside a fixed stock like the SIG behind the bolt with a sliding handle on either side for charging. The H&K trigger pack concept is excellent, but they chose the most Byzantine way to go about doing a trigger; an AR, AK, or even SIG/Beretta system would be simpler to service by about a mile. The trigger group housings are oddly tank-like, as well.

As far as the PSG-1 (don't get me started on how overrated that thing is :p), I know it has a different cam angle on its delay features, which likely accounts for its operability with the different barrel, though I think it was mainly to slow down initial recoil to aid accuracy. Roller delay can be tuned to just about anything, but I worry if for a cartridge as variable as 308 can be (110gr-200gr) that you could push past the design limits. You can do that in a Garand as well, of course, but you likely won't blow the case out in so doing (just bend the op rod). Roller delays simply have bigger consequences when they don't work right.

"I do think the H&K design could handle the power of 7.5 Swiss Ball because if you do some checking you will find in military loadings it is nearly identical in power to 7.62 Nato M80 Ball and .30-06 M1 and M2 Ball."
It's got significantly lower bolt thrust than either, IIRC (lower pressure), but has nearly identical case volume to '06, so it can get up higher in bullet weights than 308. The military GP11 is right up there with the other 30cal cartridges of the day, though (so much work by so many nations to make poor facsimiles of GP11 :(). In higher loadings with more powder, I'd worry about the extra momentum from powder gas being dumped into an H&K action; those rollers just look so tiny already, and the action was already close to margin. It'd probably work, it'd likely just wear things out faster. Ultimately, the extra powder needed to launch extra-heavy bullets from these roomy cartridges like x55 and '06 is why they were phased out; they simply aren't as 'recoil efficient' as a 308, for the types of jobs they'd be used for

TCB

PS -you didn't have to go and give away the secret to unlocking the H&K bolt head like that :D --newbies have to earn their stripes, you know ;). If you own a Steyr M95, you too will have a special hatred for bolt designs that snap down like that (no clever trick for unlocking the Steyr bolt; you gotta just grab those sharp surfaces and rip the bolt open)

briansmithwins
November 14, 2014, 04:18 AM
In theory it would seem that the HK type delayed blowback design would have the advantages of eliminating the gas system, saving weight and cost.

In practice it appears that the engineering and materials required to implement delayed blowback makes it pretty much a wash for cost and weight when compared with the M14 or FAL.

BSW

sawdeanz
November 14, 2014, 08:19 AM
In theory it would seem that the HK type delayed blowback design would have the advantages of eliminating the gas system, saving weight and cost.

In practice it appears that the engineering and materials required to implement delayed blowback makes it pretty much a wash for cost and weight when compared with the M14 or FAL.

That's about the conclusion I reached too, good summary.

So that my question doesn't derail this thread completely off topic, I present this:

https://www.youtube.com/watch?v=39tX_7-mkMA&list=UUrfKGpvbEQXcbe68dzXgJuA

The Frommer Stop pistol with a long recoil action. Pretty wacky. There is also such a thing as a blowforward pistol as well. I love the early 1900s in arms manufacture for all the great and not so great innovating they did, but at least they tried.

https://www.youtube.com/watch?v=YKo06FgXlMM&list=UUrfKGpvbEQXcbe68dzXgJuA

Nom de Forum
November 14, 2014, 11:00 AM
Century hack-jobs that are marginal at best

That is being politely understated.

As far as the PSG-1 (don't get me started on how overrated that thing is 

Hey it was great in "Sniper" making Billy Zane look like Yuppie scum trying to solve a problem with technology instead of technique.

If you own a Steyr M95, you too will have a special hatred for bolt designs that snap down like that (no clever trick for unlocking the Steyr bolt; you gotta just grab those sharp surfaces and rip the bolt open)

I once owned a Steyr M95. Yaa the bolt on the Steyr is brutally unforgiving, sometimes demanding blood for lubricant before cooperating.


Great videos sawdeanz. That Frommer is the bee’s knees. When everything works right its great, but I imagine trying to clear a feeding or ejection malfunction is nightmare. That Schwarzlose video was cool but if the video had been of a Hino-Komuro being fired it would have been an incredible find. Probably does not exist.

Carl N. Brown
November 14, 2014, 12:08 PM
I think we have drifted far away from the opening question: why the lack of recoil-operated semi rifles? A lot of comments lump recoil, gas and blowback operation with recoil operation.

In all three extraction and ejection is usually aided by residual gas pressure against the cartridge case after the bullet has left the barrel, but they are fundamentally different.

o Recoil operation has a moving barrel. Bolt and barrel are locked together during firing and recoil; the bolt and barrel recoil together and unlock after the bullet has left the barrel and the gas pressure has dropped below levels that would burst the cartridge case.

o Gas operation has a fixed non-moving barrel. Bolt and barrel are locked together before firing; the bolt is unlocked using the force of gas bled off the barrel to allow it to recoil after the bullet has left the barrel.

o Blowback operation has a fixed non-moving barrel. Bolt and barrel are not locked together. Blowback operation relies on the inertia of the bolt to keep the bolt closed until the bullet has left the barrel.

To answer why the lack of recoil-operated semi rifles? I take a sidetrack into why delayed blowback operation was pursued. Back in the early days of semi-auto rifle development John T. Thompson and John Pedersen introduced fixed barrel/hesitation "lock" rifles to avoid the complexity and expense of designs based on recoil or gas operation. Thompson used friction. Pedersen used a jointed bolt. They were not successful. The later Reising used an unlocked tipping bolt with some success as .45 M60 carbine and M50 submachinegun but the .30 carbine version never left the proving ground. Pál Király's Cristóbal design used a lever between a two piece bolt in the .30 Carbine adopted by the Dominican Republic. The StG45/CEAM Modèle 1950/CETME were eventually successful when refined as the HK G3. (However, the Reising, Cristobal and G3 do have their critics.)

What fed interest in the delayed blowback designs for military caliber rifles was the cost and complexity of competing recoil and gas operated designs. In the long run, gas operated rifle designs for high power rifle cartridges and simple blowback operated rifle designs for .22 rimfire and pistol cartridges have proven themselves less expensive and simpler than recoil operated rifle designs. The industry tends to invest in design and production based on what has been proven to work and sell in profitable volume.

The .50 Barrett M82 (M107) semi-auto sniper rifle has been the most successful recoil operated semi-auto rifle design to stay in production and to be widely adopted. But it stands alone as a successful recoil operated semi-auto rifle.

SlamFire1
November 14, 2014, 01:53 PM
I am so surprised about the dislike of the HK roller bolt rifles as I think they are an excellent military rifle. Most of the dislikes center around preferences, primarily preferences about ergonomics. As a consumer you are perfectly entitled to decide about your preferences, it is all about how you make your system trades, decide what is important to you. I remember taking a System Engineering class and the class example was a system trade on a vehicle, each group had to pick five characteristics and rank them. It was interesting to see what each group decided was the most important, the girl group, their most important preferences were all about safety, the EEO group, among their top five was “radio”, my group ignored safety, my group rated performance highest, did not care if we died in a flaming wreck, as long as we got there fast, but generally cost, reliability, comfort were in the top five of every group. However, when it came to creating priorities for employee vehicles the absolute top priority was cost and comfort was not in the top five.

The decision makers who are procuring hundred’s of millions of dollars worth of service rifles have a different priority set than an individual buying a personnel weapon. Barnbwt just assumes that whatever weapon he buys is reliable, safe, easy to maintain, but these characteristics are not necessarily so, they have to prioritized and accounted for, and built into the weapon.

I am of the opinion that the German designers of the CETME took a long hard look at their WW2 experience and prioritized cost and easy fabrication above all. You can currently buy a new PTR 91 for $1000, and the price goes up. I am surprised to see the cheapest DSA FAL is $975, the next level up is $1,700, but when the last new FN made FALs were sold in the US, they cost (adjusted for inflation) $3,000. The M14 was a very expensive rifle to build, M1a’s are not cheap, prices are not on the Springfield Armory web site, but the last I looked, a rack grade M1a was $1500-$1700. A forged receiver Rockola M14F, new, is $2,170. http://www.atlanticfirearms.com/component/virtuemart/shipping-rifles/rock-ola-m14-308-battle-rifle-detail.html?Itemid=0

Even a dollar additional cost adds up quickly for a million rifle procurement. Complaints about ergonomics are not going to be taken seriously by a group whose job is to purchase the lowest cost service rifle that meets the minimum requirements. These decision makers also have to make the trade, is it better to have all the costly niceties and slow production rate down? There will be unlucky guys who don’t get a rifle and have to carry broom sticks. Think that bothers them? :cuss: Anyone watch the movie “Enemy at the Gates”? One guy gets a rifle and the next gets a five round clip and is told to pick up a rifle from a dead companion.:eek: For all I know, that might have been true, the Russians had a heck of a time making enough equipment at various stages of the war. So did the Germans who lost Armies in Russia. Just look at the stripped down bare essentials of the Japanese and German last ditch weapons. Sure, everyone wants all the neat, costly features of an expensive weapon, but when decision makers look at National Survival and balance that against gripes about selector switch location, their top five list of desirable weapon characteristics look a lot different.

From what I understand, the HK roller bolts are the least expensive to make of any of the 308 issue service rifles, which is probably why they are still standard issue front line issue when all the other contemporary rifles, FN, M14, are not.

In theory it would seem that the HK type delayed blowback design would have the advantages of eliminating the gas system, saving weight and cost.

Ludwig Vorgrimler and his design crew certainly would have looked at gas operation but their design eliminated a number of parts, and did not require a milled receiver. Looking at my PTR91, I would say the bolt and barrel are the most difficult to make parts of the rifle, the receiver is stamped, welded sheet metal. It takes a lot less time to train someone to weld a bead than it does to train a machinist. To me, the Germans did not consider rebuild in the CETME design. Refurbishment and rebuild actually take effort from making a new rifle. I am certain they figured out they could rebuild ten rifles but with the same effort make 20 new. Compliants about requiring a manufacturing facility should not be taken seriously, just what back woods blacksmith is going to make a tank on his anvil?

In practice it appears that the engineering and materials required to implement delayed blowback makes it pretty much a wash for cost and weight when compared with the M14 or FAL.

Depends on the delayed blowback design, but when comparing the roller bolts with the M14 or FAL, the cost advantage is with the roller bolts. The less parts, the less parts you have to make, account for, spare for, have in inventory. The less parts, the better logistically. I don’t know why HK eventually dropped the roller bolt and went to a gas system for their 223 rifles.

I for one sure as heck would not want to hump a 14 pound rifle all day long. Weapon weight is not a consideration for those who drive every where, but if you are ever so unlucky to get drafted in a major war, you will find that only a few Officers get to sit on their butts and watch the country side go by. The Ground Pounder gets to carry about 100 pounds of gear and hates dragging heavy weapons around.


I got to shoot a Frommer Stop pistol, nasty sharp recoil for such a small cartridge. Also, pistol disassembly was complicated and not obvious.

Nom de Forum
November 14, 2014, 04:41 PM
[QUOTE]I am so surprised about the dislike of the HK roller bolt rifles as I think they are an excellent military rifle. Most of the dislikes center around preferences, primarily preferences about ergonomics.....

The ergonomics you dismiss so lightly can be life saving. Having your rifle inform you it is out of ammunition and it is time to reload is important and designing it to do is so easy and cheap it is ridiculous to cut that cost. Having a rifle with a safety the hinders disengagement is a real problem in reacting to an ambush. Having a rifle that is heavy and awkward to use reduces the ability of the users to gain fire superiority and is a foolish way to reduce costs.

These decision makers also have to make the trade, is it better to have all the costly niceties and slow production rate down? There will be unlucky guys who don’t get a rifle and have to carry broom sticks.


The Germans were never going to run out of rifles in the 1960s as long as the United States had millions of M1 Garands in storage.

From what I understand, the HK roller bolts are the least expensive to make of any of the 308 issue service rifles, which is probably why they are still standard issue front line issue when all the other contemporary rifles, FN, M14, are not.

Standard issue in Armys that can’t or will not pay the expense of something much better for numerous reasons.

Ludwig Vorgrimler and his design crew certainly would have looked at gas operation but their design eliminated a number of parts, and did not require a milled receiver. Looking at my PTR91, I would say the bolt and barrel are the most difficult to make parts of the rifle, the receiver is stamped, welded sheet metal. It takes a lot less time to train someone to weld a bead than it does to train a machinist. To me, the Germans did not consider rebuild in the CETME design. Refurbishment and rebuild actually take effort from making a new rifle. I am certain they figured out they could rebuild ten rifles but with the same effort make 20 new. Compliants about requiring a manufacturing facility should not be taken seriously, just what back woods blacksmith is going to make a tank on his anvil?

I think the some of the story is an example of engineering philosophy being to impress other engineers with clever and unique engineering with little thought about efficient operation by the individual user, and an unhealthy dose of NIH syndrome influencing decisions. They could probably make something like a 7.62 Nato AKM clone just as cheap. Don’t dismiss back woods blacksmithing until you examine some of the copies of rifles made in Afghanistan and Pakistan, although I don't think the complexities of making a roller delayed blowback action have been successful.

I don’t know why HK eventually dropped the roller bolt and went to a gas system.....

Because almost nobody says they want it. The most extreme example of dislike I have read is from “Testing the War Weapons”. The author, Timothy J. Mullin, after making a long list of complaints about the user unfriendliness states “Given a choice between a G3 and an M1917 Enfield .30-06, I would take the Enfield”. I wouldn’t take the Enfield but I would take just about any other modern military rifle instead.

I got to shoot a Frommer Stop pistol, nasty sharp recoil for such a small cartridge. Also, pistol disassembly was complicated and not obvious.

I envy you for the experience. :)

briansmithwins
November 14, 2014, 07:53 PM
Looking at my PTR91, I would say the bolt and barrel are the most difficult to make parts of the rifle, the receiver is stamped, welded sheet metal.

Forget the barrel, that's just a steel tube that has rifling impressed on the inside by running it through a CHF machine.

Now the bolt, trunnion, and locking piece, those are going hard to make. You need steel that's hardenable to ~56-58 RC and that's tough enough to take firing shock w/o cracking. Guys that have made new locking pieces have used high alloy steel and then surface ground the ramps the roller interface with to maintain tolerance.

Using a separate locking piece from the bolt carrier was smart, though. It let the part that needed to be massive be made from cheap carbon steel, with the locking piece effectively being a replaceable insert.

BSW

barnbwt
November 14, 2014, 07:57 PM
"Barnbwt just assumes that whatever weapon he buys is reliable, safe, easy to maintain"

I built that STGW57 myself. I take nothing for granted, and got nothing easily in that build. It was still an easier build than a G3, though ;). The G3 scales nicely in terms of mass production, but is not so easy for a small shop. Fancy dies and machined forgings require a good deal of tooling and industrial scale.

Which is why I wonder why Barrett-like rifles in "infantry" calibers* are not more common, military or sporting. Like the AR, the barrel and extension are the only parts requiring tooling, and they are easily sourced commodities, now. Everything else is largely non-structural, and only needs to hold a few critical tolerances (also like the AR, which can be made quite sloppily and still function, so long as drop in modularity isn't a priority). I think production could be as easy as an AK for the builder, but without the need for expensive/imported machined trunnions. The advantage is probably just that a small shop may be able to make it cheaper, and that it probably will run more cleanly than any gas op system (that's admittedly not a very compelling benefit ;)). Plus you get a 223 that actually gives some tactile feedback to let you know it fired :D

TCB

*Apparently my 223 rifle concept is uncannily similar to the Barrett M82 action. I may solicit MachIVShooter to make a 1/2 scale replica to go with his AR in 17WMR...:D

barnbwt
November 14, 2014, 08:03 PM
"Forget the barrel, that's just a steel tube that has rifling impressed on the inside by running it through a CHF machine"
On any other barrel, yes. But we need those blasted flutes, so it's either hammer forging or EDM (or a fluted reamer :D). Only a few shops can accomodate chamber flutes (like the US made backup barrel in 308 for the STGW). When you actually go to build one from non-OEM parts, you'll find yourself reaching for any design solution that avoids sourcing a fluted chamber reamer ;)

TCB

SlamFire1
November 14, 2014, 11:05 PM
I am so surprised about the dislike of the HK roller bolt rifles as I think they are an excellent military rifle. Most of the dislikes center around preferences, primarily preferences about ergonomics.....

The ergonomics you dismiss so lightly can be life saving. Having your rifle inform you it is out of ammunition and it is time to reload is important and designing it to do is so easy and cheap it is ridiculous to cut that cost.

I got to talk to a combat veteran of Iraq and Afghanistan about this issue. I asked him whether in the excitement of combat he could tell whether his rifle was empty, whether he could tell whether the bolt was locked back, which all lead to the issue of a quick magazine change. Speed was not something he was concerned about. I still remember the eyes of this Gent, looking at me, and his comment: “Don’t you realize that I have 16 other Soldiers with me?” Well, no I did not. I don’t have a CIB, my combat tactics come from movies, video games, and combat courses. The hero in the movie only has one hour and a half to kill all the evil guys till the movie ends and of course, he kills a lot of evil guys, quick magazine changes and all, till his shirt tears off showing his fine muscular torso after which then, he is obligated to kung fu his way to the end of the movie. But, it is all about him. One hero actor against legions of bad guys. We have all played video games and there a slow reload will get you killed, which is a bother, because you have to go back to the spawning point . Wonderful thing about video games, you get to come back, and of course, it is you, only you, against legions of bad guys. The self defense courses, these are timed events. The shooter who clears the room fastest, by himself, of course, wins.

I am beginning to think, in real life, that these tactics might actually be suicidal. Trying to clear a room, building, by yourself, with your favorite thunderstick, and to do it as fast as possible, is probably a good way to get yourself killed. I can think of a number of better options. Pull back, let the heavy machinegun perforate the place, keeping the bad guys down, while someone shoots an AT4 through the front door. Or, call in artillery, or ask the friendly skies to drop some napalm and enjoy the barbeque. Who said real battles have to be over in an hour and half?. Racing against a clock can get you dead, and in the real world, when you are dead, you don’t come back to a spawn point.

I do like my bolt hold open in my Garands, M1a’s, and AR15’s. It allows me to shoot single shot, prone with a sling, during highpower matches. But I am beginning to think, that is why it is there. The US military used to shoot KD bullseye and every rifle since the Trapdoor has features best suited to the target shooting game. The Army used to think bull’s-eye represented combat training, but that sort of went away in the 60’s. I did take my PTR91 to a local reduced course, 100 yard, across the course (XTC) match and found that it is was totally unsuited to the game. I had to load my rapid fire magazines, 3 rounds and 7 rounds. You are required to make a RF reload. Cocking the PTR requires a huge shift of position, so for sitting RF and prone RF, I fired two rounds, put the safety on, inserted the seven round magazine, and fired till the gun was empty. It was impossible to shoot 20 rounds prone slow gun empty, single shot, without breaking position, so I got permission from the match director to shoot 20 rounds from a loaded magazine. The PTR91 design is definitely not the rifle to shoot in an XTC match. But XTC is a game, and I have had fellow shooters who were combat veterans, tell me that.

But back to that bolt hold open device, my WASR does not have one. I don’t have any others, nor have I handled all the variants of the AK 47, but I suspect none of the rifles has a bolt open device and the Kalashnikov seems to be a very popular battle rifle all things considered. So maybe, a bolt hold open device is just a nice to have, not all that important outside of movies, video games, and combat course games.


These decision makers also have to make the trade, is it better to have all the costly niceties and slow production rate down? There will be unlucky guys who don’t get a rifle and have to carry broom sticks.


The Germans were never going to run out of rifles in the 1960s as long as the United States had millions of M1 Garands in storage.

Well for a time we had a rifle shortage in the early 60’s. The DCM sold a number of M1’s that were rebuilt in the early 60’s, these rifles have a penciled location and date (like RRAD 6-63) on the receiver tang. The Army did not have enough M14’s around and was rebuilding M1 Garands just in case the balloon went up. I have a bud, who was in the 82 Airborne during the Cuban missile crisis. He was in active status (which meant within 24 hours they were ready to drop anywhere) and when given the notice to ready up , he traded his M1 carbine for a M1 Garand because, as he said, the “M1 carbine was a nice gun to play solider”, but he did not want to drop on Cuba with one. His unit, in 1962, did not have M14’s, but was going to be one of the very first to be dropped in a war. His almost claim to fame was that it was going to be a race between him, and the guy on the other side of the plane, as to who would hit Cuba first. Later he found, the drop point was a killing zone for all things American. Still, I was very surprised that the first responders did not have M14’s. Given the lack of M14’s, I don’t know how many M1 Garands the US would have given up to an ally.

If you read this months "Military History" and the article about what would have happened if Russia invaded the West, anything not already in Germany, would have arrived after the Russians captured the county.

They could probably make something like a 7.62 Nato AKM clone just as cheap.

Don’t know, but the AK and its round was a very pragmatically designed weapon, and a very good one. Not adopting the AK was truly an example of not invented here.

briansmithwins
November 15, 2014, 01:48 AM
Not adopting the AK, FAL, British 6.5mm class assault rifle round, adopting the M60 and M14 and the shenanigans related to the AR15 are all very good examples of Army Ordinance's mentality about what was developed by them and therefore perfect.

When the Swiss we're looking for a replacement for the StG57 rifles they picked the AK and pretty much copied it straight across, except for the trigger mechanism.

As far as bolt hold opens go, if the Soviets (AK47), German Army (G3), and Brits (L1A1) had wanted a BHO they would have designed one in. The Brits had to delete the automatic BHO
on the L1A1 because they didn't want it. BHOs are not without demerits, they allow more garbage into the gun and are yet one more control that needs to be trained on.

BSW

Nom de Forum
November 15, 2014, 02:07 AM
[QUOTE]I got to talk to a combat veteran of Iraq and Afghanistan about this issue. I asked him whether in the excitement of combat he could tell whether his rifle was empty, whether he could tell whether the bolt was locked back, which all lead to the issue of a quick magazine change. Speed was not something he was concerned about. I still remember the eyes of this Gent, looking at me, and his comment: “Don’t you realize that I have 16 other Soldiers with me?” Well, no I did not. I don’t have a CIB, my combat tactics come from movies, video games, and combat courses. The hero in the movie only has one hour and a half to kill all the evil guys till the movie ends and of course, he kills a lot of evil guys, quick magazine changes and all, till his shirt tears off showing his fine muscular torso after which then, he is obligated to kung fu his way to the end of the movie. But, it is all about him. One hero actor against legions of bad guys. We have all played video games and there a slow reload will get you killed, which is a bother, because you have to go back to the spawning point . Wonderful thing about video games, you get to come back, and of course, it is you, only you, against legions of bad guys. The self defense courses, these are timed events. The shooter who clears the room fastest, by himself, of course, wins.

I am beginning to think, in real life, that these tactics might actually be suicidal. Trying to clear a room, building, by yourself, with your favorite thunderstick, and to do it as fast as possible, is probably a good way to get yourself killed. I can think of a number of better options. Pull back, let the heavy machinegun perforate the place, keeping the bad guys down, while someone shoots an AT4 through the front door. Or, call in artillery, or ask the friendly skies to drop some napalm and enjoy the barbeque. Who said real battles have to be over in an hour and half?. Racing against a clock can get you dead, and in the real world, when you are dead, you don’t come back to a spawn point.

I do like my bolt hold open in my Garands, M1a’s, and AR15’s. It allows me to shoot single shot, prone with a sling, during highpower matches. But I am beginning to think, that is why it is there. The US military used to shoot KD bullseye and every rifle since the Trapdoor has features best suited to the target shooting game. The Army used to think bull’s-eye represented combat training, but that sort of went away in the 60’s. I did take my PTR91 to a local reduced course, 100 yard, across the course (XTC) match and found that it is was totally unsuited to the game. I had to load my rapid fire magazines, 3 rounds and 7 rounds. You are required to make a RF reload. Cocking the PTR requires a huge shift of position, so for sitting RF and prone RF, I fired two rounds, put the safety on, inserted the seven round magazine, and fired till the gun was empty. It was impossible to shoot 20 rounds prone slow gun empty, single shot, without breaking position, so I got permission from the match director to shoot 20 rounds from a loaded magazine. The PTR91 design is definitely not the rifle to shoot in an XTC match. But XTC is a game, and I have had fellow shooters who were combat veterans, tell me that.

But back to that bolt hold open device, my WASR does not have one. I don’t have any others, nor have I handled all the variants of the AK 47, but I suspect none of the rifles has a bolt open device and the Kalashnikov seems to be a very popular battle rifle all things considered. So maybe, a bolt hold open device is just a nice to have, not all that important outside of movies, video games, and combat course games.

Feel better after getting that all off your chest? Good grief no one is claiming a bolt hold open device is necessary because of the need to be making routine “Gun Game” type rapid reloads in combat. Your combat veteran friend’s opinion is realistic in that combat is played as a team sport by those who want to live. However for him to say he was not concerned with speed in getting his empty rifle back to firing makes me wonder about the variety of his combat experiences. I don’t play video games, war movies frequently make me laugh at what they portray, I haven’t played the gun games in decades because I realized they teach to many bad/suicidal habits, and the only worthwhile combat courses I attended were courtesy of the U.S. Army. I was taught to reload a rifle as a quickly as possible so I could support those “16 other soldiers with me” to keep them and me alive. The bolt hold open feature makes that easier and even if the soldier does not immediately notice the feeling his bolt has locked back he will get the rifle back in action faster releasing it than he would having to pull back a charging handle from its forward position. This last point is especial true when compared to the gawd awful heavy and long pull of a H&K G3. By the way have you considered that a wounded soldier incapable of charging a G3 for reloading may very well be able to do so with a M16, M14, and even a FAL. Of all those rifles none of them is more in need of a bolt hold open feature than a G3. Lack of a bolt hold open device as a standard feature on the Kalashnikov has been a concern of some users and there have been attempts to correct that flaw. One of those attempts is nothing more expensive than changing out the magazine follower to one that will hold the bolt open on the last shot.

Well for a time we had a rifle shortage in the early 60’s. The DCM sold a number of M1’s that were rebuilt in the early 60’s, these rifles have a penciled location and date (like RRAD 6-63) on the receiver tang. The Army did not have enough M14’s around and was rebuilding M1 Garands just in case the balloon went up. I have a bud, who was in the 82 Airborne during the Cuban missile crisis. He was in active status (which meant within 24 hours they were ready to drop anywhere) and when given the notice to ready up , he traded his M1 carbine for a M1 Garand because, as he said, the “M1 carbine was a nice gun to play solider”, but he did not want to drop on Cuba with one. His unit, in 1962, did not have M14’s, but was going to be one of the very first to be dropped in a war. His almost claim to fame was that it was going to be a race between him, and the guy on the other side of the plane, as to who would hit Cuba first. Later he found, the drop point was a killing zone for all things American. Still, I was very surprised that the first responders did not have M14’s. Given the lack of M14’s, I don’t know how many M1 Garands the US would have given up to an ally.

That is all very interesting but irrelevant. The Bundeswehr was not lacking in arms before the adoption of the G3. The soldats were already armed with M1 Garands, G1s a.k.a. FN-FALs, and even played around with a few G2s a.k.a SIG 510s before going with the cheaper G3. I doubt the war would have lasted long enough to expend all of those but if it did the U.S. would have had time to resupply the Herms.

If you read this months "Military History" and the article about what would have happened if Russia invaded the West, anything not already in Germany, would have arrived after the Russians captured the county.

I was stationed in Germany during the 1980s and 1990. I was one of the few soldiers who did not believe the story that the war would start after a period of rising tensions followed by obviously noticed pre-combat deployments. After the fall of The Wall, I was in Berlin during the fall, documents from the East showed that the Soviet Bloc was prepared to make a significant attack on almost a moments notice with little indication that would warn the West. I was right in my belief that if my unit just happened to be already deployed the duration of my wartime mission would probably be measured in minutes before I was killed or running for my life after all our equipment was destroyed by artillery and being overrun.

Nom de Forum
November 15, 2014, 02:42 AM
Not adopting the AK, FAL, British 6.5mm class assault rifle round, adopting the M60 and M14 and the shenanigans related to the AR15 are all very good examples of Army Ordinance's mentality about what was developed by them and therefore perfect.

When the Swiss we're looking for a replacement for the StG57 rifles they picked the AK and pretty much copied it straight across, except for the trigger mechanism.

As far as bolt hold opens go, if the Soviets (AK47), German Army (G3), and Brits (L1A1) had wanted a BHO they would have designed one in. The Brits had to delete the automatic BHO
on the L1A1 because they didn't want it. BHOs are not without demerits, they allow more garbage into the gun and are yet one more control that needs to be trained on.

BSW

Apparently the Brits recognized their error in not having a BHO when they replaced the L1A1.

briansmithwins
November 15, 2014, 06:16 AM
I don't think the replacement (SA80) can be held up as a example of good design.

BSW

Nom de Forum
November 15, 2014, 11:24 AM
I don't think the replacement (SA80) can be held up as a example of good design.

BSW

Ironically it was H&K that cleaned-up the design faults to make it a good rifle.

Something else of note about BHO devices on rifles. The Israelis have one on their Tavor. Few countries have more experience using rifles in combat than the Israelis. I doubt the U.S.A. will omit the BHO on whatever rifle eventually replaces the M16 series, since the U.S. Army also has quite a bit of experience using rifles in combat. Are any new combat rifle designs, other than Russian, omitting BHO? I think the real reason some of the rifle designs since the 1940s omitted BHO was because the designs could not have an attached detachable box magazine reloaded with stripper clips and the designers never took sufficient time to consider other advantages of having a BHO feature. Some of the T48s ended up being used at the 18B school. I always thought a FAL you could reload with stripper clips was I great idea.

SlamFire1
November 15, 2014, 11:53 AM
As far as bolt hold opens go, if the Soviets (AK47), German Army (G3), and Brits (L1A1) had wanted a BHO they would have designed one in. The Brits had to delete the automatic BHO on the L1A1 because they didn't want it. BHOs are not without demerits, they allow more garbage into the gun and are yet one more control that needs to be trained on.

Whereas the Americans have a tradition of BHO devices, primarily there, in my opinion, so they could play the XTC game, the British Lee Enfield never had one, so there was not any core advocacy within the requirements group.

And this, more than anything else, is why features differ between National Armies. The members of the Joint Requirements Oversight Council (JROC) and the group that creates the Operational Requirements Document (ORD) directly decide the functional features (among many other functional characteristics) that must be in the weapon system. No particular feature gets into a requirements document without strong internal advocacy, and for every feature that someone claims is essential, there is someone else who is very skeptical of the need, particularly if it has cost associated with it. There is no Guerrilla larger than the Finance Guerrilla, and no ceiling taller than the Budget Line Item. While this turns out to be very frustrating to some end users, for example the guys who wanted a coffee grinder in the buttstock (Sharps rifle), not everyone gets everything they want in life.

I have been promised that the next life is much better, so maybe in Paradise I will get my coffee grinder back.

http://media.boingboing.net/wp-content/uploads/2014/07/1241K-JPG633536159190913576.jpg

http://www.nps.gov/spar/historyculture/images/Sharps_crank.jpg

barnbwt
November 15, 2014, 01:14 PM
The "coffee grinder" was a generic grain grinder so poorly supplied troops could make their own milled starches from produce found in the farmland they fought through. Not quite as sillyas we always make it out to be ;)

"Not adopting the AK was truly an example of not invented here."
Though not related, the AK and Garand share an eerie amount of commonality in the gas, bolt, and trigger systems

"I think the real reason some of the rifle designs since the 1940s omitted BHO was because the designs could not have an attached detachable box magazine reloaded with stripper clips"
Probably, but lots of designs also used clips themselves as the hold open for loading. What designs besides the AK, G3, and M16 couldn't take clips, though? ;)

TCB

Nom de Forum
November 15, 2014, 04:37 PM
[QUOTE]Whereas the Americans have a tradition of BHO devices, primarily there, in my opinion, so they could play the XTC game, the British Lee Enfield never had one, so there was not any core advocacy within the requirements group.

And this, more than anything else, is why features differ between National Armies. The members of the Joint Requirements Oversight Council (JROC) and the group that creates the Operational Requirements Document (ORD) directly decide the functional features (among many other functional characteristics) that must be in the weapon system. No particular feature gets into a requirements document without strong internal advocacy, and for every feature that someone claims is essential, there is someone else who is very skeptical of the need, particularly if it has cost associated with it. There is no Guerrilla larger than the Finance Guerrilla, and no ceiling taller than the Budget Line Item. While this turns out to be very frustrating to some end users, for example the guys who wanted a coffee grinder in the buttstock (Sharps rifle), not everyone gets everything they want in life.

American use of bolt hold open devices has nothing to do with "XTC games". The 1903 Springfield has a BHO device (mag follower), the M1 Garand had to have one to ensure clearance of the enbloc clip during ejection and to make reloading practical, the M14 had one, and so does the M16. Only the M16 has one for reasons other than reloading without removal and replacement of the magazine. They all have one partially for the reason of letting the soldier know his rifle is empty and to speed reloading.

As I mentioned in other words in a previous post, the British have apparently decided that a BHO device is an advantage since their current rifle has one. I am sure the cost of adding such a device is so trivial in comparison to other items of consideration that cost alone has very little to do with the decision. The problem preventing earlier adoption was most likely “if it was good enough for our (fill in the appropriate title of an ancestor) to not have them then we don’t need them”.

The "Coffee Grinder Sharps" was intentional not given to all soldiers because one was expected grind food for several soldiers. A wise cost cutting measure that in no way reduced combat effectiveness like the lack of a BHO device could in certain situations.

Nom de Forum
November 15, 2014, 05:24 PM
"I think the real reason some of the rifle designs since the 1940s omitted BHO was because the designs could not have an attached detachable box magazine reloaded with stripper clips"

Probably, but lots of designs also used clips themselves as the hold open for loading. What designs besides the AK, G3, and M16 couldn't take clips, though? ;) TCB

I consider a detachable box magazine with a follower that holds the bolt back after the last shot to be a type (poor type) of BHO device.

Clips? I assume you mean stripper clips a.k.a. charging clips, not detachable box magazines. If so the answer to your question is any design that has an upper receiver or receiver cover that blocks the vertical insertion of a clip to refill a box magazine. Besides the three you listed can be added the FAL, CAL, FNC, AUG, SA-80, FAMAS, AR70, SIG 510, and several others. Some of them though have BHO devices that are obviously not there to permit reloading of the magazine with stripper clips but to speed-up the reloading of the rifle with a detachable box magazine.

Willie Sutton
November 15, 2014, 10:03 PM
Hey Willie does that Mig you jockey around still have the 37mm installed?

Yes, one NR- 37 and two NS-23's, both designs being recoil operated as well.

Sadly all three are (of course) BATFE spec demils, with the rear of the receivers removed, but the remaining components are still installed in the jet for weight and balance reasons. I was going to mention that the Russian autocannons are all recoil operated. I've handled live ones in Poland, and you ought to see the recoil spring on a 37mm recoil operated cannon. The tooling needed to safely disassemble and assemble one is pretty impressive.

Willie

.

barnbwt
November 15, 2014, 11:21 PM
Besides the three you listed can be added the FAL, CAL, FNC, AUG, SA-80, FAMAS, AR70, SIG 510, and several others. Some of them though have BHO devices that are obviously not there to permit reloading of the magazine with stripper clips but to speed-up the reloading of the rifle with a detachable box magazine.
For some reason I'd thought the FAL had an open receiver, but I was just thinking of the FN49 (that was one of the things they changed for the upgrade, obviously). But mainly I was noting that none of the designs that saw wide adoption --nor the majority of designs coming out at the time, were even clip-capable in the first place. I agree that BHO's help speed reloading, especially when the charging handle is far away from the magazine or opposite the weak hand, but I'm not sure about the aspect of them notifying the shooter the mag is empty. I mean, I guess a locked-back bolt implies you didn't just have a misfire when you pull the trigger and nothing happens, but issue arms are (supposed to be) so reliable that a dud-strike would be a true rarity. But getting back to speed of reload issue, I'm quite positive the need for a locked bolt to speed up reloading is extremely dependent upon where/how the charging handle is located, which might explain why it seems kind of random which guns have/don't have the device. Might simply be a procurement officer's personal preference that makes the decision.

Grossly off topic, though ;)

Sadly all three are (of course) BATFE spec demils, with the rear of the receivers removed, but the remaining components are still installed in the jet for weight and balance reasons.
Yeah. That's why. ;) :D. As big as those things are, being recoil operated, I imagine they've gotta be built like CAT rock hammers. True heavy machinery. If you ever feel like buying a lot of jet fuel, I'm sure there's a market for a demilled 37mm parts kit (esp. if your barrel was from before the import ban) :cool:. I'm sure there'd be enough left over for some lead ballast ;)

TCB

Nom de Forum
November 16, 2014, 02:05 PM
[QUOTE]For some reason I'd thought the FAL had an open receiver, but I was just thinking of the FN49 (that was one of the things they changed for the upgrade, obviously).

Upgrade? Perhaps a matter of opinion depending on what side of the pond you live on. The Brits adopted a FAL (L1A1) without, in Brit nomenclature, charging clip capability. On the other side of the pond the Americans tested the FAL (T-48) with an open top receiver that, in American nomenclature, was stripper clip capable. More interesting is the Canadians adopted a FAL (C1) with an open top receiver that is stripper/charging clip capable.


I agree that BHO's help speed reloading, especially when the charging handle is far away from the magazine or opposite the weak hand, but I'm not sure about the aspect of them notifying the shooter the mag is empty. I mean, I guess a locked-back bolt implies you didn't just have a misfire when you pull the trigger and nothing happens, but issue arms are (supposed to be) so reliable that a dud-strike would be a true rarity. But getting back to speed of reload issue, I'm quite positive the need for a locked bolt to speed up reloading is extremely dependent upon where/how the charging handle is located, which might explain why it seems kind of random which guns have/don't have the device. Might simply be a procurement officer's personal preference that makes the decision.

I usually feel the physical difference of the bolt locking back after the last round before seeing it and that cues me to reload. A "misfire" would cue SPORTS.

SlamFire1
November 17, 2014, 03:43 PM
For some reason I'd thought the FAL had an open receiver, but I was just thinking of the FN49 (that was one of the things they changed for the upgrade, obviously). But mainly I was noting that none of the designs that saw wide adoption --nor the majority of designs coming out at the time, were even clip-capable in the first place

Maybe you could list more examples that did not have bolt open devices? I am aware, for really old rifles, the Mosin Nagant, the Krag, (US and Norwegian), the M1 Carbine, grease gun, AK 47, Sten gun, Schmeisser , SH41, all of the German Sturmgewehr ’s of WW2. Some of these I don’t have actual experience of handling, I don’t see a bolt release in pictures for the SH41, the Schimeisser, Bren, I see recesses cut into the receiver where the shooter pulls the bolt handle back to cock. I fired the Carl Gustav m/45, it does not have a bolt hold back device. I would be interesting in knowing what other submachine guns did not have bolt hold open devices. I looked at web accounts of the latest Chinese service rifles, they have bull pup designs that don’t have bolt hold open, then some models that do, it is obvious that a bolt hold open device is not a must have, simply a nice to have.

Cost is real, and those who ignore part cost only show their lack of a logistical background. Additional parts cost real money, no matter how much smoke is created to make it vanish, the real cost of even tiny parts is real and substantive. Let’s say a sell price for a bolt release is $10.00. Over a procurement of 6 million rifles, that is $60,000,000 in direct cost. The direct cost is actually a tiny fraction of the logistical burden of stocking the thing, accounting for the thing, subcontracting for it, storing it, maintenance procedures, gages, etc. Something that would cost $60,000,000 in direct cost would easily have a $100,000,000 life cycle cost, and I don’t see $200,000,000 of reasons for why a bolt hold open device is an absolute necessary.

Bolt hold open devices will cause malfunctions on their own. I have had a couple of lock backs on M1911’s when the magazine was not empty. I have had slide closures when the magazine was empty. I also have had bolt over rides on my AR15’s. If the AR bolt is accelerated a bit too much it will over ride the magazine follower. As such, as nice as a bolt hold open device is, it could give false positives, you think the chamber is loaded, but it is not, or it can cause a failure to fire just when you need the thunderstick to go bang. Relying on a bolt hold device can get you killed. I suspect that is why there are a number of fielded weapon systems that don’t have a bolt hold open device.

Using a bolt hold open device as a reason to reject a design appears to me, to be a phenomena of “Not An AR” (NAAR). Prior to NAARism there was “Not a Musket”, (NAM) which is why the 1873 Trapdoor came into inventory. It is the closest you can get to an 1861 Musket and still use a cartridge. The user does not like change. The user wants something better, only a little different, and totally rejects revolutionary change. Adopting a Martini Henry but loosing the side hammer, was a leap too far for the user. While the Remington rolling block had a hammer, baby does not want just any rattle, it wants its rattle, and only its rattle. Given a chance, the user will create definitions, excuses, must haves that lead to only one solution: same old, same old. You can see this in every US weapon evaluation. I read the troop evaluations on the M1911’s. At the end of each report is a recommendation that this new fangled pistol be rejected and the Colt SAA retained. Or a double action revolver, it all depended on what the user was familiar with. Pointy sticks had to be wrestled from the hands of troglodyte infantry before they would grasp stone tipped spears, and well into their retirement troglodyte NCO’s claimed that nothing was as ever good as their old pointy sticks. As can be seen from the historical record, Neanderthal tool technical was virtually unchanged for 200,000 years or more. Knuckle draggers, then and now, are not comfortable with change.


In so far as NAARism, would I trade off a bolt hold open device for simplicity and reliability. I don’t think the AR is the end of history, (for me, history ended with the M14) and even though the AR design provides an extremely fast magazine change capability, I would rather have a rifle that did not have so many magazine jams. This is one, while officiating an XTC match, I was able to take a picture of this jam:


http://img.photobucket.com/albums/v479/SlamFire/Rifles%20various/AR15/DSCF3453MagazineJam1_zpsaaf769c5.jpg (http://smg.photobucket.com/user/SlamFire/media/Rifles%20various/AR15/DSCF3453MagazineJam1_zpsaaf769c5.jpg.html)
http://img.photobucket.com/albums/v479/SlamFire/Rifles%20various/AR15/DSCF3453MagazineJamenlarged_zps20c891ff.jpg (http://smg.photobucket.com/user/SlamFire/media/Rifles%20various/AR15/DSCF3453MagazineJamenlarged_zps20c891ff.jpg.html)
http://img.photobucket.com/albums/v479/SlamFire/Rifles%20various/AR15/DSCF3455Magazineroundjam_zps11e864ea.jpg (http://smg.photobucket.com/user/SlamFire/media/Rifles%20various/AR15/DSCF3455Magazineroundjam_zps11e864ea.jpg.html)

Magazines are the greatest source of un reliability in the AR design, and it is all due to baby wanting only its rattle. You can read the historical record in the book, “US Rifle M14”. The infantry school did not want magazines, they wanted in block clips but would settle for stipper clips. They were used to a Garand and Garands were fed from incabloc clip. The infantry school claimed, that magazines were expensive, magazines were heavy, and that high capacity magazines lead to too much shooting. It was called "ammunition wastage". Shooting too many rounds at the enemy is considered wastage. Because of this the M14 has a stripper clip guide on top, the CONOPS of the day was that you were supposed to load the magazine from the top, while it was in the rifle, and if you search, you will find the term “semi detectable" magazine being used.

http://img.photobucket.com/albums/v479/SlamFire/M1a%20and%20Garand%20Receiver%20Pictures/M1aactiontopview_zps63f29274.jpg (http://smg.photobucket.com/user/SlamFire/media/M1a%20and%20Garand%20Receiver%20Pictures/M1aactiontopview_zps63f29274.jpg.html)

The FAL experiments of the time, loading from the top with ten round clipper strips, were an absolute failure, would have been a greater failure in the field, and no one adopted it. It was just an experiment to see if that would make the user happy. Stoner created lightweight, cheap, magazines thinking that would make them happy. It was not what the user wanted either, but it is what they got along with jams and misfeeds.

Sometimes the worst thing that can happen is to get what you think you want.

Ar180shooter
November 17, 2014, 10:14 PM
There have been a few successful recoil operated designs; however, they are usually more sensitive to dirt, heavier, and more complex to make than gas operated rifles. The reason you don't see more is that better systems have been developed. Gas pistons with rotating bolts have proven themselves as the best combination for lightweight and reliable autoloading rifles.

briansmithwins
November 17, 2014, 10:19 PM
Gas pistons with rotating bolts have proven themselves as the best combination for lightweight and reliable autoloading rifles.

Don't forget cheap. By locking a rotating bolt into a barrel extension you eliminate the need for a receiver that can take the firing stress.

BSW

Ar180shooter
November 17, 2014, 10:24 PM
Don't forget cheap. By locking a rotating bolt into a barrel extension you eliminate the need for a receiver that can take the firing stress.

BSW
True! I forgot to mention cheap. When you use a barrel extension, you can manufacture the rest of the receiver out of stamped steel (like the Sig 550) or an aluminum forging milled to final shape (like an Ar-15).

briansmithwins
November 17, 2014, 10:39 PM
When you use a barrel extension, you can manufacture the rest of the receiver out of stamped steel (like the Sig 550) or an aluminum forging milled to final shape (like an Ar-15).

Or plastic, like the ARX.

BSW

barnbwt
November 18, 2014, 01:04 AM
"The reason you don't see more is that better systems have been developed. Gas pistons with rotating bolts have proven themselves as the best combination for lightweight and reliable autoloading rifles."
Nah, I prefer to think of gas operation as merely a path we've chosen to follow for the time being; there is undoubtedly always something better out there. I think it remains to be seen whether or not recoil operation can be competitive, since we've only had a scant handful of attempts, themselves fairly primitive, and one 'modern' design, the Johnson, that was arguably an equal to any contemporary but for a few meager differences (note I said differences; a bayonet can cause failure to feed, but hot ammo won't exactly break a Johnson's not-an-op-rod, either). Given what has been learned about recoil systems, combined with what we've found is good, bad, and useful regarding gas systems and service/commercial rifles in general, it stands to reason a modern recoil operated gun could be designed that has many advantages of its own.

I think even rotating bolts won't stay around forever (I think falling-block automatics will eventually be developed, at which point a gun's length will be limited to the barrel plus the cartridge length)

The barrel extension concept is here to stay; it's physically impossible short of some alien-tech solution like magnetic or ionic bonding to hold the breech shut using a smaller/shorter means. What's beautiful about this concept, though, is practically any design there is can use a barrel extension in some fashion, so long as the bolt locks at or near the front. The structural receiver was only ever needed in designs locked at the tail of long bolt bodies (BREN) or for more modern designs being manufactured with antiquated techniques (Garand).

But back to recoil operation;
I've done some more research/asking around, and I think I've found a very compelling idea; basically it's a 1/2 scale Barrett M82. The Barrett uses leverage to throw the lighter bolt back faster than the barrel, so that heavy mass does not need to bounce nearly so much in order for the action to cycle reliably. Normally, that's why these guns kick so hard; the bolt plus barrel have to be going at the "escape velocity" when they unlock in order for the bolt to cycle completely. If leverage dumps some barrel momentum into the bolt as it parts ways, less recoil energy is needed to run the gun in the first place.

This is why gas-op guns have been so prominent; very efficient use of operating force to run the action. Early gas-ops had huge pistons, and were enormously overgassed. The gas port in the Hotchkiss Portative was like 2/3 the bore diameter. The piston was more than the barrel diameter, if memory serves, all for a LMG cartridge :eek:. If it wasn't so gawdawful heavy, the operating recoil had to have been insane. But, designers rapidly learned they could easily regulate and efficiently exploit the gas pressure, and designs have used and less and less of the total energy available to operate the gun since. The result is the lightest parts traveling the smallest distances at the slowest speeds, culminating (for now) with the H&K MP7, which is a teeny tiny AR-180 action powered by the meager gas volume of a PDW cartridge (albeit a hot-rodded one).

My point is, if a recoil operated gun can be similarly efficient in how it uses the recoil of a shot to cycle the gun, I wager it can be similarly effective, while also offering distinct advantages, disadvantages, and differences that all add up to more options for a shooter to select from.

What I foresee is a tube-based aluminum receiver setup with hand guard-length barrel shroud, using off-the-shelf AR barrels/extensions/bolt head assembly, mags, and FCG (if not complete or modified lower). The muzzle-half of the barrel would be exposed just like any other AR design, and the overall profile of the main receiver ('upper' if you must) would not be unlike the current DI art. What is different is how much hugely simpler it would be to make with more primitive facilities.

The operation would borrow elements from the Barrett "bolt accelerator" concept, but instead of direct mechanical leverage linking the bolt/barrel, a spring would be differentially charged between them, unloading its stored energy (the bulk of the recoil experienced by the barrel) into the bolt body upon unlocking. Designed appropriately, recoil would be less than for an unbraked DI action. Initial recoil goes into a soft recoil spring and towards charging the accelerator spring instead of the shooter's shoulder. By the time the barrel hits its stops, the bullet is both long gone and the barrel has lost nearly all its momentum. At that point, the bolt would require the same inertia as an AR to complete its circuit. So, you have a softer-recoiling rifle that moves around slightly more (maybe) between shots owing to its larger, but slower moving, cyclic mass. It is entirely possible the setup would have an insanely high cyclic speed, too (that's fairly common for short recoil actions, but of course highly dependent on the unique dynamics of a given design)

Advantages would probably be similar to what they are in pistols; large degree of flexibility in both ammo and barrel lengths, so long as the reciprocating elements can be buffered (or braked) sufficiently. Suppression would likely be better over a gas system, so long as the system can be boosted sufficiently. Depending on how the spring accelerator is designed, it would actually cushion the bolt head as it returns to battery, which could only help both felt recoil and operating noise. Good chance it'd be cleaner than a DI, or possibly even long-stroke gas systems, too.

Disadvantage would be that, yes, if you rest the non-shrouded portion of the barrel on something, or attach a bayonet, you would affect the cycle. Charging the gun would likely be a bit odd; you can either draw the bolt straight back and drop the barrel partway during the pull, or initially unlock the bolt through some other movement before pulling it back. There would also likely be a longer lower limit on barrel length, since buffer spring stiffness would have to skyrocket to protect the action as the barrel got lighter and lighter. That, or you'd require more and more obnoxious muzzle brakes for an SBR build :eek:. The big disadvantage would be people calling the gun a "Stoner's Johnson" :neener:

TCB

sawdeanz
November 18, 2014, 11:29 AM
The Barrett uses leverage to throw the lighter bolt back faster than the barrel, so that heavy mass does not need to bounce nearly so much in order for the action to cycle reliably.

This just reminded me about the existence of the Russian AN-94, which I'm pretty sure is recoil operated. It has a smaller lighter bolt that reciprocates twice as fast as the barrel, enabling it (with some other gimmicks) to fire 2 shots before the recoil of the barrel hits the shooter.

Actually looking it back up it is actually gas operated for some reason, but it still shows that there is at least one military that is considering a rifle with reciprocating barrel. I don't know why a similar design couldn't be incorporated with pure recoil-operation, since the AN-94 is clearly to complicated for serious work, especially with both disadvantages of gas and recoil operations.

Nom de Forum
November 18, 2014, 01:51 PM
[QUOTE] I looked at web accounts of the latest Chinese service rifles, they have bull pup designs that don’t have bolt hold open, then some models that do, it is obvious that a bolt hold open device is not a must have, simply a nice to have.

So as an example of deciding the value of paying for the inclusion of a Bolt Hold Open feature you choose rifles designed based on the values of the Chinese Army. The Chinese Army historically has little experience being outnumbered and needing to use every possible advantage to increase individual rate of fire to gain fire superiority. The Chinese Army historically does not share a concern for the lives of individual soldiers anything like that of the United States and other western democracies. The Chinese Army historically is willing to use massive numbers of soldiers in a charge to overwhelm opponents regardless of casualty percentages no western democracy could accept. The Chinese are not a good role model for emulation in combat rifle design or combat tactics for western democracies. Neither are the Russians. Both since the 1970s are emulating the design philosophy of the M16 (lighter weight, smaller caliber, better ergonomics) more than western designers are emulating Russian and Chinese design philosophy. The Chinese are apparently still sorting out the fact that just because Russians left off BHO it is not something to be copied or used to inspire new designs. The Czechs and Yugos figured that out long ago with the Vz58 and Yugo M64.

Let’s say a sell price for a bolt release is $10.00. Over a procurement of 6 million rifles, that is $60,000,000 in direct cost. The direct cost is actually a tiny fraction of the logistical burden of stocking the thing, accounting for the thing, subcontracting for it, storing it, maintenance procedures, gages, etc. Something that would cost $60,000,000 in direct cost would easily have a $100,000,000 life cycle cost, and I don’t see $200,000,000 of reasons for why a bolt hold open device is an absolute necessary.

Bolt hold open devices will cause malfunctions on their own. Relying on a bolt hold device can get you killed. I suspect that is why there are a number of fielded weapon systems that don’t have a bolt hold open device.

Bolt hold open devices are very reliable, very mechanically simple, and very inexpensive to manufacture and install on a rifle. So reliable that most modern semiautomatic pistols have them and that trend is evident in modern service rifle designs post 1950. Malfunctions are very rare. It is far more likely you will be killed in some combat situations because you are unaware your rifle is out of ammunition than because of a BHO device malfunction. The expense of adding a bolt hold open feature is probably less than 1% of the total cost of a large contract for rifles. In the U.S. Army the M16 bolt catch, pin, plunger and spring is almost never in need of replacement. The main problem with malfunctions is due to not taking bad magazines out of service soon enough. Bolt over-rides are not caused by BHO devices. Not using good quality, undamaged magazines is what causes over-rides. Over-rides can happen with any autoloading magazine fed firearm. You will get no argument from me defending the compromised design of M16 magazines but even an AK with its well designed magazine can experience an over-ride.

Using a bolt hold open device as a reason to reject a design appears to me, to be a phenomena of “Not An AR” (NAAR). Prior to NAARism there was “Not a Musket”, (NAM) which is why the 1873 Trapdoor came into inventory. It is the closest you can get to an 1861 Musket and still use a cartridge. The user does not like change. The user wants something better, only a little different, and totally rejects revolutionary change. Adopting a Martini Henry but loosing the side hammer, was a leap too far for the user. While the Remington rolling block had a hammer, baby does not want just any rattle, it wants its rattle, and only its rattle. Given a chance, the user will create definitions, excuses, must haves that lead to only one solution: same old, same old. You can see this in every US weapon evaluation. I read the troop evaluations on the M1911’s. At the end of each report is a recommendation that this new fangled pistol be rejected and the Colt SAA retained. Or a double action revolver, it all depended on what the user was familiar with.

Magazines are the greatest source of un reliability in the AR design, and it is all due to baby wanting only its rattle. You can read the historical record in the book, “US Rifle M14”. The infantry school did not want magazines, they wanted in block clips but would settle for stipper clips. They were used to a Garand and Garands were fed from incabloc clip. The infantry school claimed, that magazines were expensive, magazines were heavy, and that high capacity magazines lead to too much shooting. It was called "ammunition wastage". Shooting too many rounds at the enemy is considered wastage. Because of this the M14 has a stripper clip guide on top, the CONOPS of the day was that you were supposed to load the magazine from the top, while it was in the rifle, and if you search, you will find the term “semi detectable" magazine being used.

The FAL experiments of the time, loading from the top with ten round clipper strips, were an absolute failure, would have been a greater failure in the field, and no one adopted it. It was just an experiment to see if that would make the user happy. Stoner created lightweight, cheap, magazines thinking that would make them happy. It was not what the user wanted either, but it is what they got along with jams and misfeeds.

Your origin story of the 1873 “Trapdoor” is all wrong. The Trapdoor system was adopted because it permitted initially cost efficient conversion of existing muzzle loading rifles after the Civil War. The British did the same thing prior to the adoption of the Martini-Henry. Your comments about the Trapdoor, Martini-Henry, Remington Rolling Block, 1911, M14, FAL, and M16 are out of context and inaccurate resulting in distortion of history. Frankly, there is so much distortion needing correction I just don’t have the desire to spend so much of my time correcting them. Slamfire1 you can post errors with a few words faster than I can make the necessarily long worded corrections. Your point of view on bolt hold open devices is on the wrong side of history. Whatever future designs are created they will more likely than not have some type of device, other than failure to fire after pulling the trigger, that notifies the user the rifle is empty.

SlamFire1
November 18, 2014, 02:04 PM
Nah, I prefer to think of gas operation as merely a path we've chosen to follow for the time being;

I agree, Armies and design groups have biases. After reading enough on the early history of firearms, I found statements that lead me to conclude the Germans did not "like" gas operation and the historical evidence of their firearms makes me conclude they had a bias against gas operation. I recall reading a statement to the effect that gas operation caused erosion around the gas port, which it does. And so what. But, that was just one of the excuses used by the Germans. The majority of their machine guns and assault rifles were delayed blowback.

Paul Mauser's M1905 was a short recoil, his M1916 automatic rifle was a delayed blowback and it required greased cartridges to function. I suspect Mauser did not try to make a gas operated rifle because he knew it would not sell.

I think it remains to be seen whether or not recoil operation can be competitive, since we've only had a scant handful of attempts, themselves fairly primitive, and one 'modern' design, the Johnson, that was arguably an equal to any contemporary but for a few meager differences (note I said differences; a bayonet can cause failure to feed, but hot ammo won't exactly break a Johnson's not-an-op-rod, either). Given what has been learned about recoil systems, combined with what we've found is good, bad, and useful regarding gas systems and service/commercial rifles in general, it stands to reason a modern recoil operated gun could be designed that has many advantages of its own.

I agree, just don't know if other than same old/same old is the reason why everything has gone gas operated.

Nom de Forum
November 18, 2014, 02:07 PM
Given what has been learned about recoil systems, combined with what we've found is good, bad, and useful regarding gas systems and service/commercial rifles in general, it stands to reason a modern recoil operated gun could be designed that has many advantages of its own.


barnbwt,

I think there will continue to be much resistance to recoil operated combat rifles because of concerns about moving barrels, lack of need for flexibility to fire cartridges of greatly varying characteristics, user experienced shooting characteristics, and most importantly no significantly greater advantages prior to the adoption of radically new small arms technology. If a new combat rifle design used recoil for operation it would have to be incredibly better than existing gas designs to change the minds of procurement authorities.

Ar180shooter
November 18, 2014, 03:38 PM
"Nah, I prefer to think of gas operation as merely a path we've chosen to follow for the time being; there is undoubtedly always something better out there."

I feel this should be qualified. There is always something better out there when new technology is developed. I'm not convinced there is something that improves on gas operated, piston driven lightweight automatics. A new recoil driven design may improve on some aspects, but as long as we are using brass cased ammunition, I do not think any advantages will outweigh the disadvantages of adopting such a system.

"I think it remains to be seen whether or not recoil operation can be competitive, since we've only had a scant handful of attempts, themselves fairly primitive, and one 'modern' design, the Johnson, that was arguably an equal to any contemporary but for a few meager differences (note I said differences; a bayonet can cause failure to feed, but hot ammo won't exactly break a Johnson's not-an-op-rod, either)."

There were lots of attempts in the early days, few were successful in military firearms, most were unsuccessful. They were, quite simply, inferior to gas operated arms. The Johnson was an interesting design, but it was fragile, unreliable and expensive to produce compared to the Garand. It was not comparable, because you could arm multiple soldiers with the more reliable Garand for the same cost as 1 Johnson.

"Given what has been learned about recoil systems, combined with what we've found is good, bad, and useful regarding gas systems and service/commercial rifles in general, it stands to reason a modern recoil operated gun could be designed that has many advantages of its own."

The Beretta/Benelli inertia system is an example of this. It is appropriate for sporting arms. For military arms, it is not sufficiently robust and reliable.

"I think even rotating bolts won't stay around forever (I think falling-block automatics will eventually be developed, at which point a gun's length will be limited to the barrel plus the cartridge length)"

Possibly, but probably not. The big issue that I can see with a falling block automatic is the extraction and reloading cycle. You would need separate pieces to remove spent casings and insert new cartridges. By using caseless ammunition, you do remove the extraction cycle, but this still doesn't completely relieve the problem. Such a mechanism would have to be quite complex. This takes away from reliability, and adds to cost and weight. In addition, modern gas operated firearms are more than sufficiently compact. The biggest advances in the next 25 years will be in material technology, lightening already light designs.

"But back to recoil operation;
I've done some more research/asking around, and I think I've found a very compelling idea; basically it's a 1/2 scale Barrett M82. The Barrett uses leverage to throw the lighter bolt back faster than the barrel, so that heavy mass does not need to bounce nearly so much in order for the action to cycle reliably. Normally, that's why these guns kick so hard; the bolt plus barrel have to be going at the "escape velocity" when they unlock in order for the bolt to cycle completely. If leverage dumps some barrel momentum into the bolt as it parts ways, less recoil energy is needed to run the gun in the first place."

How is any of that an advantage over a gas operated firearm? Such a system is not any less expensive, lighter or more reliable than a gas operated system in conventional light arms.

"This is why gas-op guns have been so prominent; very efficient use of operating force to run the action."

They are efficient and modern ones are very light weight.

"My point is, if a recoil operated gun can be similarly efficient in how it uses the recoil of a shot to cycle the gun, I wager it can be similarly effective, while also offering distinct advantages, disadvantages, and differences that all add up to more options for a shooter to select from."

It's not just about being able to operate the gun. I'm quite sure one could develop a recoil operated small arm that can compete with the M16 in almost every way... except cost would be astronomical and there would be no practical advantage.

"What I foresee is a tube-based aluminum receiver setup with hand guard-length barrel shroud, using off-the-shelf AR barrels/extensions/bolt head assembly, mags, and FCG (if not complete or modified lower). The muzzle-half of the barrel would be exposed just like any other AR design, and the overall profile of the main receiver ('upper' if you must) would not be unlike the current DI art. What is different is how much hugely simpler it would be to make with more primitive facilities."

A DI system on something like a stamped Ar180 upper/lower would be much simpler.

"The operation would borrow elements from the Barrett "bolt accelerator" concept, but instead of direct mechanical leverage linking the bolt/barrel, a spring would be differentially charged between them, unloading its stored energy (the bulk of the recoil experienced by the barrel) into the bolt body upon unlocking. Designed appropriately, recoil would be less than for an unbraked DI action. Initial recoil goes into a soft recoil spring and towards charging the accelerator spring instead of the shooter's shoulder...."

The Barrett system is not inexpensive as it requires very precise tolerances to be reliable. Not exactly something you want in an inexpensive and easily produced arm. That's the thing about gas operated firearms... they can be reliable, even with loose tolerances. This is why I don't think any other system will replace them until radically new technologies are developed.

"Advantages would probably be similar to what they are in pistols; large degree of flexibility in both ammo and barrel lengths, so long as the reciprocating elements can be buffered (or braked) sufficiently. Suppression would likely be better over a gas system, so long as the system can be boosted sufficiently. Depending on how the spring accelerator is designed, it would actually cushion the bolt head as it returns to battery, which could only help both felt recoil and operating noise. Good chance it'd be cleaner than a DI, or possibly even long-stroke gas systems, too."

What are you basing any of that on? Seriously, you're just making most of that up without any real evidence to back it up.

"Disadvantage would be that, yes, if you rest the non-shrouded portion of the barrel on something, or attach a bayonet, you would affect the cycle. Charging the gun would likely be a bit odd; you can either draw the bolt straight back and drop the barrel partway during the pull, or initially unlock the bolt through some other movement before pulling it back."

So, why would anyone want to develop such an over-complicated and temperamental beast again?

briansmithwins
November 18, 2014, 08:08 PM
In theory recoil operation eliminates parts (gas piston, op rod) and doesn't have problems with gas port erosion or fouling in the action.

In practice, the extra parts that recoil actions require (barrel mount, buffering, heavier/more complex receiver) eliminate the weight advantage, the problems with gas port erosion aren't significant (before the barrel is shot out), and fouling hasn't been a bad problem since black powder and corrosive primers.

Gas operation isn't perfect, but the alternative is usually worse.

BSW

barnbwt
November 18, 2014, 09:23 PM
Man, this is where I hate the "Forum" format in regards to technical discussion. Everybody dissects everyone's multiple arguments sentence by sentence, which they made in a single post in the first place because that's the only practical way to make a complex/multi-point statement about something like a firearm action with many technical details. The result is the number of points made by each poster is literally multiplied by the sum of all those that came before it, and the thread collapses under its own weight (I'm thinking of that thread about the dynamics of the 1911's operation, here. I think Nom was present for that Battle Royale :D)

:banghead::banghead::banghead:

Please try to bear with me, AR180; I'll try to answer/rebut a lot of your points, but there's no way we can all hit all of eachothers' and keep the thread usable

"There is always something better out there when new technology is developed"
I agree, but since I'm kind of talking about a new technology with regards to recoil operation (since obviously the current art is inferior), this is kind of a redundant statement. Maybe not "new" as in revolutionary, but at least more evolved than a 30-06 Johnson rifle. The Garand fails in practically the exact same ways in comparison to the M16 (or anything else), and it was really not much different in execution than the Johnson (meaning the materials, desired usage/features, overall layout, and "state of the art" that correlates all contemporary designs with the eras of their creation)

There also seems to be some misunderstanding about such a new concept making its way into an issued arm (or rather, our issued arm). There's no way some new technology is gonna overcome the internal bias, idiocy, and illogic infecting our --or any-- procurement process to 'win the day' solely based on its technical merits. It's fun to think about what would be the best for our boys, but it's a foregone conclusion that they won't be getting it, except by accident. So I'd much rather keep the 'practicality/realistic use' discussion centered more on the commercial side of things, which biased though it is, does seem to respond more readily to legitimatly good ideas. Most of the time. I'm aware all the modern competitive tactical shooters more or less desire the same feature set as soldiers, which is fine, but the procurement angle is a discussion area I simply can't comment on because of both ignorance and irrelevance to recoil operation itself.

"There were lots of attempts in the early days, few were successful in military firearms, most were unsuccessful. They were, quite simply, inferior to gas operated arms."
This was hardly the case prior to WWII, and not even necessarily the case by the end of WWII. The main thing the war proved to everyone, was that gas ports really don't amount to a hill of beans, and that gas operation is fine if you have non-corrosive ammo (or take appropriate provisions against corrosion). I'd argue that WWI was actually the war that proved bolt guns needed to go bye-bye, but the second war came too quickly for everyone to have upgraded fully. And l like I said before, I think gas systems are more easy to 'tune' during development than recoil operation, since their timing variables are independent of the geometry (weight) of the functional parts. That means you can delay or speed, lighten or embolden, and precisely meter exactly how the gun cycles from the gas block. Basically, if you design a straight-pull bolt action that works reliably, you are basically guaranteed a gas system can be fitted to it and run well.

Recoil operation is inherently dependent upon its particular set of components to cycle. Arbitrarily decide to make the barrel too heavy in the early design phase --won't work without a recoil booster that makes the gun kick hard. Make the bolt travel too short based on an initial guess early on, and the gun may cycle too fast for the magazine. These things are much easier to tune/time on a gas operated design, but require very significant changes to a recoil design. Changes that themselves have ramifications.

But simply because recoil operation may be harder to get right, does not necessarily mean that it yields inferior results. The end product is what matters, right? Let's at least assume that a properly tuned recoil action can be developed for whatever hypothetical scenarios we can conjure, just as I'll assume any supposed Stoner action is properly tuned (that one took a while to get right, as well)

"The Beretta/Benelli inertia system is an example of this. It is appropriate for sporting arms. For military arms, it is not sufficiently robust and reliable."
I had a Franchi I12 shotgun using this action. The only gun I sold, and for 2 reasons; 1, the gun did not fit me well at all; happens to everyone with every gun. 2, the gun jumped around like crazy as part of its necessary operating cycle. The problem with the inertia system, is that the shooter becomes a critical part of the recoil tuning balance equation. I tended to be either too heavy or too rigid for the gun to cycle properly (I plant myself firmer than I probably should when shooting clays), forcing me to actively loosen my shouldering of the gun; no bueno (ouch). It's bad enough that a long recoil system slams the bolt+barrel directly into the shooter through a frame and buffer; the inertia system slams the whole dang rifle into your shoulder. So you must either have a really squishy bad, or wimpy pectoral muscles, or stand with your feet somewhat close together so your upper body can rock around like a punching clown

"The big issue that I can see with a falling block automatic is the extraction and reloading cycle. You would need separate pieces to remove spent casings and insert new cartridges."
Technically, you need separate pieces for those functions in a reciprocating bolt design as well. They just move as a unit in that format, whereas in a FB, they don't. PM me if you are actually interested about this concept, since it's really outside the scope here (I shouldn't have brought it up as conjecture)

"How is any of that [Barrett accelerated-short-recoil] an advantage over a gas operated firearm? Such a system is not any less expensive, lighter or more reliable than a gas operated system in conventional light arms."
I'm no expert, but I suspect the Barrett is quite a bit lighter than some of the gas-operated 50cal rifles out there with same-class barrel lengths/profiles (granted, the Barrett is a bit of a pig, since that undoubtedly helps the gun cycle more efficiently, so perhaps not). It's hard to find whether posted weights are loaded or not (makes a big difference on a 50cal), but even the DI Serbu 50cal* is only about 5lbs lighter unloaded (I don't know if the Barrett weight online is w/ mag or not). At any rate, it doesn't appear to be a major difference at least for that type of rifle with such large barrel:overall weight ratio.

As far as cost and reliability, I won't claim to know how much a non-existent hypothetical rifle would chart ;). Barrett seems to think they are the only player out there*, and that would possibly give a reason for the massive cost differential over the Serbu (Barrett-10000$; Serbu-7000$). But as far as simplicity, I'm working on a design similar to what I've described; it looks like the spring-loading function I describe can be effected with a single rotating collar about the chamber area and a single stiff spring to drive it (there would be no need to cushion the barrel assembly itself with another spring). Still a work in progress, I know, but theoretically you only need a single additional moving component over a typical short-recoil to make the concept work. More work is still needed on the particulars, though...

"They [gas-op guns] are efficient and modern ones are very light weight."
But lets keep in mind why they are both efficient and light. Early gas guns that managed to actually work well, like the Garand, were not exactly great in either area. Eventually, advances in materials (aluminum and sheet metal) and mechanical design (short stroke operation, the barrel extension concept, modularity as a design goal) yielded the AR180; arguably the dead end (or 'culmination' if that sounds better) of the piston-operated gun development path. Subsequent improvements in materials like polymer have not been nearly as marked an improvement (see again ARX-160), and very little as far as modularity or ergonomics/layout has changed much at all.

Apply the '50's love of large caliber, select-fire, LMGs to the Johnson rifle (along with some terrible Israeli execution :p) and you get the ill-fated DROR light machine gun. Apply the same exact materials advances and design goals as the AR10/AR15 to something like the Johnson rifle, and you would obviously expect something far different to come out than what we've seen so far. I, personally, have not seen convincing proof/reasons/arguments for why such a result could not be an improvement. Partially because proving a negative is impossible (:P), partially because I'm a technological optimist when it comes to guns, and partially because what I do understand about recoil operation strongly suggests it carries a set of strengths and weaknesses just like gas operation, and none of them inherently precludes an effective design execution.

"I'm quite sure one could develop a recoil operated small arm that can compete with the M16 in almost every way... except cost would be astronomical and there would be no practical advantage."
Care to elaborate, specifically? Would the barrel bushings make it cost tons more, or the two return springs? Because that's basically all there is to a recoil action that isn't also in a gas-op action (they both need a receiver tube, bolt, and trigger group). What you'd lose is the gas block, gas port, gas tube, bolt carrier in its entirety, and the need for a complex CNC machined upper receiver. The lower would basically be unchanged, unless you opted to roll the buffer tube into the now completely tubular upper receiver for additional simplicity at the cost of reduced modularity.

I'm not saying I positively disagree with you --I can't since there's no recoil rifle design to actually compare to-- I just don't see the likelihood of enormous additional complexity or cost. Now, the rotating-breech H&K G11 with its caseless baloney, that carries some pretty obvious intrinsic costs over pretty much every action type that's been tried.

"A DI system on something like a stamped Ar180 upper/lower would be much simpler."
Putting aside the honest question of why no one's tried that yet (seriously; why hasn't anyone? That's a legitimately good concept to pursue, and a pretty obvious one, to boot. All the new short stroke piston guns blatantly crib off the AR180, so why not DI?), stamped receivers and are actually pretty hard to make without tooling. Anything more complicated than the AK's two straight bends basically needs to be farmed out to a full-on press house. For an industrial undertaking, that's not a big deal, but I like to be able to build my guns (I know, not a concern to most, but a real one to me). If 80% builders and build parties are any clue, there is actually a real demand out there for a quality, home-buildable rifle platform that doesn't rely upon foreign-sourced parts that are both artificially cheap and finite in supply.

Picturing how both concepts could be laid out, I think they'd be rather similar in complexity: a non-structural trunnion holding the AR180 barrel/gas system set into the front of the receiver shell, with your return springs extending back to a non-structural rear trunnion (built into the upper or the lower), all sitting atop a self-contained lower. The recoil rifle would have the barrel assy sitting inside the receiver tube, guided by a few cam pins in slots, or something, with a recoil spring extending back to the removable end cap, all sitting atop a self-contained lower.

They're different, but not totally far off in terms of relative complexity. At least in parts count, the recoil action likely has fewer, but its not like the extra parts of a short stroke tappet action are all that complicated anyway. If a DI gas system (AR or the simpler/messier AG42) were used, I'd think the moving parts would be fewer, but the total number about the same. I just think it's too close to definitively call for any modern, modular design with a non-structural receiver. At least not until more specific designs are being considered. It's not like recoil vs. gas-piston operated pistols where it's a night/day difference for any number of reasons.

"The Barrett system is not inexpensive as it requires very precise tolerances to be reliable. Not exactly something you want in an inexpensive and easily produced arm. That's the thing about gas operated firearms... they can be reliable, even with loose tolerances."
The Barrett is also firing a very powerful cartridge with very grave consequences if things don't work right. "Service" rifles do too, but it's still quite different as it relates to 223 class cartridges. 223 doesn't require anything close to the kind of dwell time as 50bmg in order to unlock the breech safely, nor the momentum required to extricate a stuck case and feed a new one. In order to do those things without overpowering the shooter by putting more recoil into the system, all the parts must be high quality so no energy is wasted. There's nothing particularly special about the feed, extraction, or lockup operations themselves that necessitates especially precise manufacture compared to other mechanisms. I think the 'sniper' accuracy requirements are more the driving factor, there.

Gas operated guns can be reliable with loose tolerances, but only by 'over gassing' the system. The AK is the most well-known example. This occasionally manifests itself in blown off gas covers :D. The trouble is, in order to drive the "loose" guns hard enough to cycle reliably, you must impart a lot of needless energy into guns at the nominal or "tight" areas of the spectrum. That means your pistons must be tougher, your gas tubes/blocks stronger, your frame buffering more capable...basically you have to bulk up the rest of the gun so it can run rougher without breaking.

I would also argue that, at least with the present state of the art, the axiom does not apply to direct impingement guns. The fact is that deviation from nominal tolerances seems to have an outsized effect on Stoner gas systems compared to others, with piston rings, gas tubes, bolt carrier weights, and buffer springs requiring tweaking when the design must operate in non-optimum conditions (short barrel, suppressor, bad piston/bolt tolerance, bad gas port size). The main thing the Stoner design has going for it in this regard, is that it is so easy to discard & replace the offending portion of the puzzle and replace it with another that probably won't show the same variance. It works great on a large, well supplied scale (or one where parts suppliers want to make it rich :D), but can be very frustrating to a home builder or smith seeking to modify a functional design. Not everyone's concern, I know, but my/many others' preference tends towards adaptability vs. disposability

"What are you basing any of that [supposed recoil operation advantages] on? Seriously, you're just making most of that up without any real evidence to back it up."
Maybe I should have elaborated; back in that ginormously-long and intense 1911 discussion I alluded to earlier, we all realized through the power of math that recoil operation is very self-regulating so long as you can adequately buffer the system. To shoot a bullet heavy enough to unlock the gun earlier solely by virtue of its additional mass, it had to be more dense than Uranium :eek:, and anything less dense would eat up your powder volume with the extra bullet length required. Conversely, lighter and lighter bullets are limited in how much recoil can be imparted to the action by the mass and peak velocity than be attained by the powder itself and a theoretical 0gram bullet; as I recall, such a situation cannot generate enough 'oomph' to unlock the gun. In short, the conclusion was that recoil actions do not need to be timed for different loads the same way as gas systems are. The catch is in cushioning the hard-recoiling situation while maintaining reliability for the lightest bullets possible. Do keep in mind this was for 45acp; 223 is neither fat nor stubby, so those limits may not be as absolute (probably not in the case of heavy bullets since there is so much powder capacity)

Also, once more, expecting me to present real-world evidence for a theoretical exercise that, again, does not exist, is a bit unfair. The best I can do is examine the physics/kinematics of such an operating concept, and posit how they would seem to differ from currently available gas operated actions. The purpose is to ponder how such a non-existent technology might differ from what we have now, so we could then debate/ponder whether or not it constituted an improvement or not. A 223 with a recoil impulse that is possibly 'smoothed out' but possibly a bit higher overall seems like it could potentially be attractive. It could feel like a roller-lock gun but run cleaner; what's not attractive about that?

"So, why would anyone want to develop such an over-complicated and temperamental beast again?"
No one's asking you to; you'd just be buying it ready-made. Maybe that's the issue, here. I'm sensing some outright hostility to the very concept as presented, with very few specific reasons justifying blanket statements like "it can't" or "it won't". FWIW, even those dead-simple blowback pistols took years to develop, and the locked-breech designs took professional design houses with many engineers/inventors even longer. Those early experiences and research has at least formed a 'road map' for present designers, so we can at least take an efficient path to a design solution instead of flailing randomly (with Blish locks and rifling-torque :D). Compared to other dead-end concepts like toggle lock, tilting bolt/flap, blowback, blow-forward, and gas traps, recoil operation looks downright sensible.

Neither the Garand nor the Johnson were the 'best gun' for WWII (see: FN49), but the Garand is what we took to the dance, and forever colored our biases with. Just as the manually-operated guns colored future preferences for undrilled barrels ("why, those barrels have to be 30 inches long to shoot accurately. They could never tolerate such a disruption as a gas port. No we don't understand the effects of pencil barrels and wooden forestocks on accuracy" :banghead:). The fact there is such a demonstrable cause for bias in the firearms design (that's not even getting into whether or not it is actually impacting the designs out there), and the fact that recoil operation works stunningly well for a certain class of firearm (pistols), and the fact that all firearms technology has evolved substantially since recoil rifles were last tried, strongly suggests they at least warrant a thorough examination for viability.

If they're still not a contender, I vote we check again in fifty years to see if they're better for shooting the standard caseless ammo at renegade cyborg bodies, or better for whittling out with files in caves to combat The Rise of the Machines, or for integrating into a do-all cybernetic arm :D (all three sides of the fight, there :evil:)

TCB

*"As the first and only semi-automatic .50 caliber rifle available..." --Barrett M82 webpage :rolleyes:

barnbwt
November 18, 2014, 09:34 PM
"Gas operation isn't perfect, but the alternative is usually worse."

Agreed. Definitely the case thus far, anyway. But it's just so darn effective in semi-auto pistols...there's just gotta be some sort of utility in other areas of the design space. Like I wrote (somewhere in the sea of that last post :D) above, it's possible that advances in other parts of firearms tech, like ammo, materials, and design conditions, have made the recoil action more attractive than when it was last tried.

After all, you try pitching an early gas operation to German generals when ammo was corrosive and barely reliable. Jams galore, corrosion, complication, a real pain the rear to operate compared to a bolt gun, that's for sure. Heck, try pitching a perfected AR relying on aluminum to Germans prior to WWI :D

"In practice, the extra parts that recoil actions require (barrel mount, buffering, heavier/more complex receiver) eliminate the weight advantage, the problems with gas port erosion aren't significant (before the barrel is shot out), and fouling hasn't been a bad problem since black powder and corrosive primers."
I'm picturing/working on an extruded tubular aluminum receiver with a couple simple slots to guide the internal parts on. Hard to argue its more complicated than the hot mess that is the AR receiver in its 'evolved' form. The thing's about as elegant as a Krag at this point with that forward assist :D. Yes, I'm aware that complex machining has become less of an obstacle in recent years to industrial manufacturers, but that's hardly an argument to say it does not matter at all. Considering both designs use a circular-profile bolt/barrel of the same size, the receiver would be very similar from the chamber back; and from the chamber forward, don't most modern AR's have an aluminum tube for a hand guard extending to the gas block? ;)

Would there be areas where complexity increases? Undeniable. Would there be others where it disappears? Probably.

TCB

Jim Watson
November 18, 2014, 10:55 PM
Anybody want to revive the primer setback action?
The Garand design didn't work well when they went to MR and IMR powders more progressive than Pyro DG. But surely our rocket scientists can adapt.

SlamFire1
November 18, 2014, 11:08 PM
Recoil operation is inherently dependent upon its particular set of components to cycle. Arbitrarily decide to make the barrel too heavy in the early design phase --won't work without a recoil booster that makes the gun kick hard. Make the bolt travel too short based on an initial guess early on, and the gun may cycle too fast for the magazine. These things are much easier to tune/time on a gas operated design, but require very significant changes to a recoil design. Changes that themselves have ramifications.


I broke out my Brassey's and looked at the section on short recoil. The author called the MG42 mechanism, a roller bolt, short recoil, accelerator mechanism, an extremely efficient mechanism. I also browsed my book on the roller bolts and something I think germane to this discussion is the amount of analysis that goes into designing a successfully "half locked" delayed blow back mechanism. The book "Full Circle" shows some of the force diagrams. At least for the roller bolt, calculations for mass, angles, forces, the kinematics of the system, is quite involved. This has to be carefully done or the mechanism will either have too much energy, or too little. Gas operated systems, you can move the gas port up and down the barrel, change the port size, there is more leniency after preliminary design to twiddle with things.

So, maybe that is one reason recoil mechanism are not that common, it takes more work up front!

Just looked at the FAMAS mechanism. It is not a gas mechanism, nor is it a short recoil mechanism, Wiki calls it a lever delayed blowback. This is one of the few service rifles that is does not use a gas operated mechanism. Nor does it have that "militarily essential" bolt lock!

Mman
November 18, 2014, 11:42 PM
There would be more recoil operated rifles if they didnt have to have minimum 16 inch barrels. The longer the barrel the more problems you have with recoil operation in a rifle that is intended to be carried and fired by one person. If short barreled rifles had a mass market (no nfa bar to over the counter sale) then recoil operation would be much more feasible. Less length and weight of barrel slamming around means simpler and more reliable. That is why it works so well on pistols.

barnbwt
November 19, 2014, 12:01 AM
"So, maybe that is one reason recoil mechanism are not that common, it takes more work up front!"
That's my working theory
"There would be more recoil operated rifles if they didnt have to have minimum 16 inch barrels."
That's my other working theory :D

How sweet & simple would a recoil-locked SBR in a super-hot PDW cartridge sized for minimal overpressure in the barrel be? The MP7 is supposedly quite unpleasant to shoot because its little gas components have such a tiny window to do their thing, that they must accelerate/collide extremely violently. They also have way too short a barrel for the cartridge they chose, so overpressure is terrible (as is erosion I have to assume). Probably the reasons that steaming pile has 6000 round service life, too :neener:

An action that is initially 'cushioned' from the shooter by the recoil spring, is truly locked breech, maintains minimal muzzle overpressure, and is as reliable as recoil pistols have proven to be, would be pretty sweet as a defense or plinking gun :cool:. Probably even more fun on full auto :evil: (not that we'd do that without a proper SOT/license ;))

TCB

briansmithwins
November 19, 2014, 02:12 AM
Recoil works in pistols because for them, it's the cheap/simple choice.

The Browning short recoil, telescoped bolt* design pistol works great on pistol caliber cartridges. It's easy to make, cheap, and strong enough to hold together for the typical life of a pistol. Scaling short recoil up to handle a rifle cartridge, not so much.

On rifles like the AR, SCAR, AK, or ARX the highly stressed components are the barrel, barrel extension, and bolt. The gas piston, cylinder, and bolt carrier are stressed too, but aren't exposed to the full peak pressure of the cartridge. Because it's cheap, tough, and strong pretty much everyone makes these out of steel.

On those designs the receiver mostly just hold the stressed components in the right place and guides them as they move around. Aluminum, sheet steel, or even plastic will work.

A short recoil rifle adds to the stressed parts the barrel buffer/recoil mechanism, and the receiver also need to handle the stresses of stopping the barrel, and maintaining the bolt lock until gas pressure falls. You either are going to wind up with a much larger barrel extension (made out of steel) or a steel receiver.

BSW

*Yes, Browning invented the telescoped bolt decades before it was applied by the CZ Model 25 or Uzi: http://en.wikipedia.org/wiki/Telescoping_bolt

barnbwt
November 19, 2014, 09:42 AM
"...the receiver also need to handle the stresses of stopping the barrel, and maintaining the bolt lock until gas pressure falls."
I'd be using an AR barrel/extension. All the reciever does is guide their relative translation/rotation. Even an AR upper/lower has to handle the recoil forces. The tube would be under no greater strain than the takedown or hammer pin seats. That is, so long as recoil doesn't need to be amplified for function. I agree the Browning tilt barrel lockup would be untenable, here. This is more like the Barrett, Lynx, or possibly PX4 to a limited extent.

TCB

briansmithwins
November 19, 2014, 10:00 AM
I'd be using an AR barrel/extension. All the reciever does is guide their relative translation/rotation.

What stops the barrel extensions rearward motion? What stops counter recoil?

7075 aluminum is very strong for its weight, but it isn't hard. using it as a impacting surface against steel is going to lead to a very short life.

BSW

barnbwt
November 19, 2014, 10:55 AM
Barrel bushing woukd likely either hit a crosspin or come to the end of a slot to arrest its movement. With any sort of buffer spring or material, this would be no more violent than the AR's resistance of its barrel's movement; same recoil force driving the numbers. What stops counter recoil in an AR when the bolt hits home? What I'm saying is, I imagine these loads coukd be quite a bit larger than the AR's without being an issue, and even if they were, some quick reinforcement would likely overcome it.

As much as people bag on the R51, the steel hitting the little aluminum shelf under bolt thrust is a lot more durable than they'd expected. Some erosion due to the sliding motion at the edge, but no peening or shearing is ocurring on mine/others.

TCB

Nom de Forum
November 20, 2014, 02:16 AM
I broke out my Brassey's and looked at the section on short recoil. The author called the MG42 mechanism, a roller bolt, short recoil, accelerator mechanism, an extremely efficient mechanism. I also browsed my book on the roller bolts and something I think germane to this discussion is the amount of analysis that goes into designing a successfully "half locked" delayed blow back mechanism. The book "Full Circle" shows some of the force diagrams. At least for the roller bolt, calculations for mass, angles, forces, the kinematics of the system, is quite involved. This has to be carefully done or the mechanism will either have too much energy, or too little. Gas operated systems, you can move the gas port up and down the barrel, change the port size, there is more leniency after preliminary design to twiddle with things.

So, maybe that is one reason recoil mechanism are not that common, it takes more work up front!

Just looked at the FAMAS mechanism. It is not a gas mechanism, nor is it a short recoil mechanism, Wiki calls it a lever delayed blowback. This is one of the few service rifles that is does not use a gas operated mechanism. Nor does it have that "militarily essential" bolt lock!


Slamfire1,

You are right about the FAMAS, but you should look at more than the mechanism of the FAMAS because it could be enlightening. The French always do things a little different with varying degrees of success. Some of the cause of this a national characteristic of needing to be very distinctly French to differentiate themselves from, and occasionally claim cultural superiority over, the rest of the world. Prior to 1981 the French were using the MAS 49/56 7.5x54, a DI gas system operated combat rifle that is one of the most reliable and durable combat rifles ever made by any country. Here is where the distinctly French thing occurs; weirdly the 49/56 does not latch on to magazines, magazines latch on to 49/56s. What is not distinctly French or weird is the 49/56 has a last shot bolt hold open as a feature. In 1981 the French replaced the 49/56 with the MAS FAMAS 5.56x45, a lever delayed blow-back operated combat rifle that is not one of the most reliable and durable combat rifles ever made by any country. In addition to foolishly not installing a last shot bolt hold open device they spent the money that could have paid for it on designing and buying a proprietary 25 round box magazine instead of using M16 magazines. The French also built the FAMAS with poor quality plastic furniture and operating parts that quickly broke in the field. That was only the beginning of the consequences of lack of forethought and poorly thought-out decisions. A decade later the French having identified several deficiencies and disadvantages fielded the improved G2 version of the FAMAS. One design feature of the new G2 was use of STANAG, essentially M16, magazines. This decision was made after having to cooperate with NATO during Operation Desert Storm. Of course there is just one small fly in the ointment for cooperating with NATO in using those STANAG magazines. The FAMAS does not like NATO ammunition. The root cause of this goes back to the distinctly and weird French decision to use a delayed blow-back operating system in the FAMAs that, despite using a fluted chamber like the H&K G3, frequently tears the heads right of brass cased NATO ammo. The FAMAS uses French steel cased ammunition to prevent this malfunction. This is the consequence of choosing an operating system that time has shown to be unpopular with most nations and will probably never be used again in a new combat rifle design.

So now the French as of 2014 have realized that the FAMAS must be replaced with something better and more NATO ammunition compatible. Many of the current rifle designs they will be considering have a last shot bolt hold open feature just like the old reliable MAS 49/56 the FAMAS replaced. I would not want to have to bet that the next combat rifle the French adopt will not have a last shot bolt hold open feature. I would bet that most French soldiers will be pleased to have that feature back after a three decade absence from the standard issue combat rifle. Oh, by the way, some elite French police units and military special operations units already use combat rifles that have a last shot bolt hold open feature.

barnbwt,

Here is your great opportunity. The French are looking for a new combat rifle design. Being French they are not afraid to gamble on something distinctly different, since they love the advant garde. This is the nation after all that fielded the first smokeless powder combat rifle (Lebel), and fielded the first accurate recoil compensated quick firing field gun (French 75mm). Now is the time for you to convince the French, that with your paid help of course, what they need and could have is a state of the art long recoil operated combat rifle. It will be even easier to convince them if you tell them it can be a bull-pup so they will not worry the World will think they are admitting a mistake for going bull-pup with the mediocre FAMAS. You do need to realize though that if you and the French create a successful rifle the Germans, British, and Americans will steal the idea and make a better rifle. At least that has been the pattern for over 100 years. Personally I think the French should have skipped the FAMAS and redesigned the MAS 49/56 using more modern materials, reduce its size and weight for 5.56, use a non-steel receiver with steel inserts for high pressure areas, and dump the weird self-latching magazines.

As a side note of long recoil operation, Jane’s mentions it only has one advantage. That advantage is "reducing the forces" on gun mounts for larger weapons. I suppose they are implying long recoil operation spreads out the recoil force over a longer period of time to avoid a wrenching jolt to the gun mount. Perhaps what they mean by stating long recoil has only one advantage is that is the only advantage not canceled out by other disadvantages, and characteristics equaled by other operating systems.

P.S. barnbwt if the French take you up on a long recoil rifle I would like a piece of the "action" for suggesting it to you.;)

briansmithwins
November 20, 2014, 04:27 AM
Another disadvantage of long recoil is that in fully automatic weapons it leads to slow ROF.

Your maximum ROF is limited to how fast the action cycles.

BSW

Nom de Forum
November 20, 2014, 12:47 PM
Another disadvantage or long recoil is that in fully automatic weapons it leads to slow ROF.

Your maximum ROF is limited to how fast the action cycles.

BSW

That is probably not much of a disadvantage for a combat rifle unless you are striving for an extremely high, before full recoil, burst mode. So far designs striving for that have not been very successful in being adopted as the primary combat rifle of any nation. Any possible slow ROF on long recoil actions in full automatic mode for close range and suppressive rifle fire could be somewhat compensated for by adoption of short/fat cartridges, telescoped cartridges, and the holy grail a.k.a. caseless ammunition with all the advantages of cased ammunition but none of the disadvantages of all previous caseless small arms ammunition. Elimination of ejection could possibly facilitate faster return of the breech block into battery.

sawdeanz
November 20, 2014, 01:22 PM
Yes but short recoil action has a faster ROF, as evidenced by the MG42.

Nom de Forum
November 20, 2014, 02:06 PM
Yes but short recoil action has a faster ROF, as evidenced by the MG42.


A Browning AN/M3 .50 cal using a long recoil action has just as fast a ROF as a MG42.

briansmithwins
November 20, 2014, 08:11 PM
MG42s do have a high ROF, achieved in part by the muzzle booster.

None of the M2 variants that I'm aware of ever got anything like 1200-1500 rounds per minute ROF with any decent reliability. And the base M2 design is short recoil, not long.

BSW

Nom de Forum
November 20, 2014, 09:35 PM
MG42s do have a high ROF, achieved in part by the muzzle booster.

None of the M2 variants that I'm aware of ever got anything like 1200-1500 rounds per minute ROF with any decent reliability. And the base M2 design is short recoil, not long.

BSW

The Browning AN/M3 is a modified M2. It was intended for aircraft use and was the product of research started before WWII to increase rate of fire. At the very end of WWII some U.S. fighter aircraft were armed with the AN/M3. By the time the Korean War began U.S.A.F. fighters such as the F-86 Sabre had it as standard armament. Unfortunately by that time it was obvious 20mm and larger cannon were really needed to be effective because .50 caliber bullets had become insufficiently effective in air to air combat. This is something the U.S.N. realized in WWII and had already armed their post-WWII fighters with 20mms prior to combat in Korea.

barnbwt
November 22, 2014, 02:42 AM
"The French are looking for a new combat rifle design. Being French they are not afraid to gamble on something distinctly different, since they love the advant garde. This is the nation after all that fielded the first smokeless powder combat rifle (Lebel), and fielded the first accurate recoil compensated quick firing field gun (French 75mm). Now is the time for you to convince the French, that with your paid help of course, what they need and could have is a state of the art long recoil operated combat rifle."
Yo no hablo francais. I could pitch at the Spaniards, but they're even broker than the French, these days. :D I expect the frogs will go with the ARX, precisely because it is the cheapest option out there from a NATO country (and, it's still a fairly decent weapon, after all --they could do worse).

I still think long-recoil's ship has sailed. Aside from very specialized high recoiling applications where you want as long a time to hydraulically damp out that heavy recoil as possible (see: cannon) so to avoid damaging fixed mounts, there don't seem to be many advantages. It's like long-stroke vs. short stroke pistons; having the extra reciprocating mass moving around in tandem is nice to guarantee authoritative cycling, but that extra authority is really just at the expense of far greater recoil. Authority you could get by simply accelerating the smaller bolt faster in the first place (provided your magazine can keep up) or designing the gun to be less prone to binding/blockage. Past some point I think it's foolish to force an action (as with the forward assist, if the inertia of a bolt body running full-tilt isn't enough to strip or chamber a round, there's probably something terribly wrong :eek:), but I also recognize there wasn't much alternative in the early days of autoloaders, when guns typically had obnoxiously close fitment and tons of openings for debris ingress. Toss in the terrible lubricant/park finish/mag designs of the day, and you had a whole lot steeper hill for the action to climb than nowadays with our Boron and Teflon coatings.

As far as slow short stroke actions, recall that recoil op pistols tend to have extremely high rates of fire. Bubba'ed 1911's frequently clock north of 1000 rounds per minute, which I think only the MAC11/9 comes close to in terms of stupid-high bullet spray. FAMAS is also ridiculously high, if memory serves. I imagine the highest rate of fire attainable is far more a function of how strong and well buffered the back of your receiver can be, than your chosen operating system ;)

Nom,
I don't know jack about the AN/M3 (sounds cool, though), but what I suspect is that the reciprocating mass was reduced a bunch in order to increase ROF --that's just basic mass kinetics, after all-- but that this had the unfortunate effect of opening the action way too early to be safe. So they increased the length of dwell time to where the action could unlock safely once more. Iterate this process more than once, and you realize that if you hold the dwell time as long as your parts' length allow (i.e. long recoil), you can crank of the ROF as fast as your parts' geometry will let you. However, the side effect is absolutely hellacious recoil; not only are the barrel/bolt slamming to the rear in tandem, they are also going as fast as the action can possibly accommodate without unlocking early. That's what the fancy damping systems were for; I bet the aircraft superstructure only "felt" every other shot from the guns since the whole system was carefully tuned like a car suspension. Very compelling for a mounted gun, but that recoil might well be untenable for an infantryman.

A double-shot burst setup using the same premise and a hydraulically damped stock might be kind of cool, though (I bet it'd be wildly impractically heavy, though)

Since I don't plan on going to the trouble of eking out an existence in the cut-throat world of gun manufacturing, here's a rough animation of my accelerator-collar concept;
http://i1159.photobucket.com/albums/p630/barnbwt/Recoil%20Cycle_zpsewuddmxt.gif
As you can see, the accelerator adds exactly one additional part to the mix. The stiff spring is the same one that returns the barrel forward; there is not really any reason the barrel & collar need to return forward on their own, since the bolt will drive them back anyway (not shown is a relief in the collar so it clears the magwell no matter its position/orientation)

I like it since it looks easy to make :D. Aluminum tube receiver, steel tube accelerator collar, and a steel pin in the receiver to cam it (can't really see the inclined cam surface cut on the back side of the collar, but it's there). I'll order one of those nifty cooling-finned AR barrels (http://www.gmriflebarrel.com/gm-m11-finned-barrel-in-5-56mm-with-ext/) Green Mountain is selling --to go with the retro sub-gun look-- and some 1.25ID & OD tubing for the receiver/collar. I've already sourced a bolt assembly and have a PSA AR15 LPK that can be worked into a modified lower. I think some savvy shopping, and lucky guesses during design (to limit the redesign iterations) could keep costs below 300$ for the project :cool:

If it blows a case (I'll be remotely firing it for testing ;)), just make another tube with the unlocking cam incline moved further back, and try, try again :p

TCB

PS: yeah, the spring compression and contact mechanics aren't perfectly accurate yet; bite me :neener: (learning this new CAD program has me on edge. I'll eventually figure out how to use the animation/simulation module)
PPS: The attached is the overall receiver layout; to cock, you can either pull straight back and pull the barrel, or pull up first and then back to manually disengage the lugs. Shown is a full length M16 barrel model, a carbine would be shorter and have a shorter shroud section. Stick an AR15 lower under it, and that's pretty much what it'll look like

TCB

Nom de Forum
November 22, 2014, 03:05 AM
Very cool barnbwt! I am off to bed as I have an early start for a drive to California tomorrow. I'll get back to you though when I can as I think you tentative design is very interesting. Don't let not speaking French detour you from pitching to the Frogs as far more of them speak english than they are willing admit. Appeal to their vanity for embracing the advant garde and they will speak english.:D

briansmithwins
November 23, 2014, 03:30 AM
Couple of questions:

1) Looks like you’re using the receiver for a opening cam. If the receiver is aluminum and the cam pin/CH is steel, it seems like the receiver will have a very short life.

2) The bolt looks like it’s locked to the barrel extension/insert. But it looks like the barrel extension/insert is only attached to the barrel by a spring. Is that correct?

It looks like the barrel recoils, and then the barrel extension/insert recoils and cams separately. What drives the insert movement and camming?

BSW

Elkins45
November 23, 2014, 09:22 AM
Couple of questions:

1) Looks like you’re using the receiver for a opening cam. If the receiver is aluminum and the cam pin/CH is steel, it seems like the receiver will have a very short life.


BSW

Cast or pin a hardened bearing surface into the receiver, then put a roller around the cam pin.

barnbwt
November 23, 2014, 10:17 AM
1) There's a roller bearing on the charging handle to prevent galling, and the accelerator (dark grey collar about the barrel extension) keeps the barrel/bolt from having to recoil as fast while locked together --the spring only discharges once the cam is fully up the ramp. The ramp will also be pretty shallow to further reduce contact loads. I think hard anodizing or powder coating would be tough enough for a good, long time.

2) The bolt and barrel/extension are standard AR15. The dark grey piece stays stationary while the other parts recoil, compressing a spring against the barrel extension until the bolt unlocks. The accelerator collar is held stationary since it can on move along a helical path, and the bolt handle blocks its rotation until it is unlocked. That's why the collar around the barrel extension stays in place initially.

The goal was to harvest accelerator energy from the initial recoil phase as opposed to from barrel overtravel after unlocking like the Barrett, so the heavy barrel has to move as little as possible.

TCB

barnbwt
November 24, 2014, 09:09 PM
Ordered the 'fancy' finned barrel and tube-stock, so hopefully I'll be on my way soon. Made a trade for a bolt head assy, and hopefully will make another for a firing pin. I've got the AR trigger parts, already.

I'll start by making an aluminum receiver for the proof of concept phase (hmm...not sure how to simulate recoil for a short-recoil action without subjecting it to actual recoil --gotta figure something out for that), and a DOM steel double for at least the initial run. The steel is mostly to try to contain an OOB rupture to some degree during remote test fire while I verify the action timing is safe. Once that is shown good, I can swap the parts into the aluminum tube and see if it starts galling/peening off the bat.

I suppose I'll still need to source a buffer spring, and of course I need to settle on how to do the lower. If anyone's got an aluminum ~80% they screwed up the buffer tower on, I'm all ears :)

Oh, one thing I'm going to try on this build; polymer bolt body. The bolt head is stuck into a cylindrical body that fits the larger receive tube diameter, which would normally make the bolt assembly very heavy if made from steel (or even aluminum, really). I bought some Delrin and UHMWPE rod to drill/turn to size. Neither would be as good for sustained fire as metal, obviously, but this is a semi-auto, after all. I suspect the high lubricity of both will somewhat negate the tendency to gall against the much harder metal parts, and Delrin at least, has very good thermal stability. The UHMWPE was mostly as a backup in case the Delrin is too brittle (both are very cheap compared to metal, too)

TCB

Nom de Forum
November 25, 2014, 11:37 PM
Nom de Forum -
A Browning AN/M3 .50 cal using a long recoil action has just as fast a ROF as a MG42.


MG42s do have a high ROF, achieved in part by the muzzle booster.

None of the M2 variants that I'm aware of ever got anything like 1200-1500 rounds per minute ROF with any decent reliability. And the base M2 design is short recoil, not long.

BSW

You are indeed correct about M2 variants being short recoil operated and I suffered a serious headspace and timing problem with the post on the AN/M3 .50 because it is indeed a short recoil operated MG and does not support the contention that a long recoil operated MG could achieve just as hight of ROF as an MG42. That post was made too late at night and somewhat influenced by my default reaction that the MG42 is somehow special in having the capability of a 1200 round ROF since the AN/M3 does it without a muzzle booster. I still suspect a long recoil action could achieve a ROF more than sufficiently high for a full automatic rifle.

Nom de Forum
November 26, 2014, 12:27 AM
barnbwt - The goal was to harvest accelerator energy from the initial recoil phase as opposed to from barrel overtravel after unlocking like the Barrett, so the heavy barrel has to move as little as possible.


Wow you are a busy man considering you are still working on this project last I checked in!

http://www.thehighroad.org/showthread.php?t=750964

How is the little carbine going since your last post in mid-October?

Oh, one thing I'm going to try on this build; polymer bolt body. The bolt head is stuck into a cylindrical body that fits the larger receive tube diameter, which would normally make the bolt assembly very heavy if made from steel (or even aluminum, really). I bought some Delrin and UHMWPE rod to drill/turn to size. Neither would be as good for sustained fire as metal, obviously, but this is a semi-auto, after all. I suspect the high lubricity of both will somewhat negate the tendency to gall against the much harder metal parts, and Delrin at least, has very good thermal stability. The UHMWPE was mostly as a backup in case the Delrin is too brittle (both are very cheap compared to metal, too) TCB

Why bother with trying Delrin first instead of the UHMWPE? Perhaps I am mistaken due to my limited knowledge but doesn’t the polyethylene have far more going for it than the polyoxymethylene? It is after all so tough that it is “bullet proof” when used in armor and I think even more resistant to chemical degradation. For a semi-automatic it may very well be in your application just “just as good for sustained fire as metal”.

barnbwt
November 26, 2014, 01:07 AM
"Wow you are a busy man considering you are still working on this project last I checked in!"
Nah, I just excel at wasting time, so much that I can waste time on multiple pursuits simultaneously :D

"How is the little carbine going since your last post in mid-October?"
The Skorparev is still rocking out where I left it, but things plateaued about the time I needed to drill the first hole :D. I actually have a small bench-top drill press now, so I will be revisiting it probably after the New Year. Also still trying to come up with something I like for attaching the removable barrel. First, I'm trying to finally knock out the M90 shotgun mod/build, that's been taking up space for two years (it's getting there; see attached). I came to the conclusion that I need to actually finish a couple of my projects to free up Tupperware bins for new projects :P

"Why bother with trying Delrin first instead of the UHMWPE?"
Depending on exactly how "ultra high" the molecular weight is, polyethylene can be a soft/waxy material (think milk jugs) that wouldn't be the best option for this application. Just how the polymer is processed also has significant impact on properties (the mer chains are so long, the stuff is almost like a fiber composite, and the orientation/organization of the strands determines bulk properties). The site said low impact resistance, so I was also a bit uneasy about it smacking the rear of the receiver tube, as well as the cam pin set into it bearing against the cam track abruptly (not an impact, but close). Delrin seems to be pretty consistently hard stuff, but also brittle. I did buy some aluminum bar stock as a fall-back-fall-back, though. I think Delrin is also a thermoset, rather than a thermoplastic, so not as many worries about operation at elevated temperature.

I did get my metallic stock for this project today, so we're on our way. It does appear I'll need to turn down the 1.25" diameter stuff that rides inside the receiver; it's not quite telescoping in the larger tubes (by like a thousandth)

TCB

barnbwt
December 1, 2014, 08:40 PM
Got most of my remaining materials in today, namely the barrel --Snoopy dance! :)

I have to say, these Green Mountain ringed barrels are pretty cool; I have no idea why they aren't showing up in more ultralight builds (cuts for the rings aside, they are actually a pretty narrow profile across their length).

Looking at the barrel in relation to the receiver tubes (which are 1/4" larger than the barrel extension flange), the proportions are quite a bit different from what we're used to in a 223 AR platform. I think the overall size is about the same --after all, free float tubes seem to be in the 1.5" OD range-- but it looks way fatter due to the circular vs. 'tall' profile.

However...

I think I can make this work to my advantage in an incredibly cool way. Behold;
http://24.media.tumblr.com/e8d08f7ab25a226d8b3c6ea50110d5d7/tumblr_mjvnxgDBDA1s57vgxo3_1280.jpg
The VG1 'last ditch' gas-delay rifle also has a fat-pipe receiver with a little pencil barrel nosing out the front (the protruding barrel on mine is nearly a foot, though), but still looks cool owing to the beefed-up "submachinegun" profile. I think the ringed barrel would look awesome with that, especially if I forgo the AR components in the lower and use 223 AK magazines & a sheet metal FCG box/grip on the bottom.

On the other hand, if I instead use a modified AR lower, there are plenty of advantages as well. The mags automatically sit much higher so they can feed into a tubular receiver situated above, like mine. Same goes for the hammer design. I think there wouldn't be a whole lot more work besides chopping off the buffer tower. I don't think the looks would be quite so striking, but with a Beta drum, I can't help but think this would look like a smaller MG15 w/ doppeltrommel.

http://media-cache-ec0.pinimg.com/736x/7d/86/b2/7d86b287a690f650639546b20266c864.jpg

Any thoughts as to one or the other?

TCB

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