technical discussion for the function and design of self-loading rifles


April 29, 2012, 12:52 PM
hey everyone.. im just making this thread for myself, and people looking to debate the various aspects of a self-loading rifle... different types of actions (blowback, recoil, gas), different materials, construction methods, calibers, etc....

i would like to know what you would think of as the perfect semi automatic, if in your own image you were able to design one?..


first off, i would like to know other peoples opinions and feelings about gas operated (long and short gas piston systems), recoil operation (long, like a browning auto 5, and short like a johnson 41, or handgun) as well as blowback, standard blowback, and the various delay mechanisms such as roller, and lever delayed... and for gas and recoil operated systems, what type of locking mechanism do you like most (rotating bolt, tilting bolt, etc)

what do you think would be the best operation in your opinions and why?


i would also like to know what type of feeding mechanism you think is best.. box magazine, internal or external... helical, rotary, belt, as well as what magazines of already existing rifles you like most?.. ar-15 mags, AK mags, etc..


im also curious what you guys think about one piece furniture such as those used on the garand, M1A, mini-14, and SKS, vs the seperation of forearm, grip, and stock such as those on the AR-15, AK, FAL, ect


i would also like to know how you feel about the different calibers available... if you prefer lighter, more plentiful ammunition, such as 5.56 or 7.62x39, or if you believe the added range and stopping power of a .308 to get more done with fewer rounds is the better way to go?


and lastly, if anyone else could think of any other features or ideas, feel free to discusss them

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April 29, 2012, 02:02 PM
There is no "best" of any of the items you mentioned. Every one of them is a compromise, and the "best" will depend upon the specific scenario you are tasked with or wish to discuss. Every one of them is "best" at one thing, and worst at something else that one of the others is "best" at.

Good luck with your discussion!

April 29, 2012, 02:16 PM
oh, i know the pros and cons of different designs, been working on various ones in 3D, i was looking for opinions and discussions on the different types...

for example, blowback design, such as lever or roller delayed is a very simple design resulting in a lighter rifle, however, the bolt does move prior to the bullet leaving the barrel, and is dirtier in general.... but without a long gas system, the bullet is usually already out of the barrel before the gas enters the tube and acts upon the piston/carrier, and is easier to fine tune, and less picky about load pressures

April 29, 2012, 03:45 PM
Start off by reading Chinn's The Machine Gun, all 4 volumes are available online in .pdf.

(If you run into Vol. 5 send me a link, I haven't read that one yet.)

Yes, all self powered firearms are a series of design compromises. What will blow your mind is that pretty much every way of carrying out the cycle of self loading was invented before WWII.

The other interesting item is that there are only two ways of designing a self loading firearm: gas operated and recoil operated.

Blowback? The cartridge case is a one use gas piston, forcing open the bolt.


April 29, 2012, 05:12 PM
this thread is to further discuss the tradeoffs, whether you may thing one tradeoff is worth another and so forth...

and about most systems being designed before WWII... we had a service rifle for just about every action in service at one point or another during WWII.... bolt action in the 1903, long stroke piston in the garand, short stroke piston in the carbine, blowback in the thompson, and even short-recoil operated in the 1941 johnson rifle...

ive actually designed a few rifles myself in 3D.. but of course they use one of these features or another... the one im working on now is a .308 caliber lever-delayed blowback that once finished will look similar to the M82 barrett rifle, but scaled down and obviously sharing zero features besides general appearance (entirely by chance)

April 29, 2012, 11:59 PM
The perfect rifle for me would be a short-stroke gas piston operated rifle with the barrel mounted with an AR-15 style barrel extension, the stock in line with the bore, a flat top picatinny rail, a curved magazine well with drop-free mags, either a chrome lined or nitrided bore, chamber and gas piston, an adjustable gas block, a front sight attached to the end of the barrel right at the muzzle, lightweight modular handguards, and chambered in a nice high-BC, intermediate power, tapered-case cartridge like .280 British.

The reason I like a short-stroke gas piston is that it can work just as reliably as a long-stroke gas piston action, but it has less reciprocating mass, which helps with accuracy.

April 30, 2012, 10:49 AM
And, DI offers even less reciprocating mass - but there's a limit, or it becomes too light to reliably strip the first round. Bolt bounce becomes a problem if you speed it up.

Compromises entail finding the optimum middle ground of operation.

Let's not forget how the barrel is attached the receiver, too. In that regard, the Stoner design offers a lot of versatility, as it eliminates the receiver - barrel attachment and reduces it to a bolt lug extension only, which screws on and adjusts the head space much like a micrometer. No press, no fuss, no muss.

Entirely why you can build a highly accurate AR on the kitchen table. Literally. And part of why they have run off piston operated conventional receiver actions in precision shooting.

Choosing from a menu of different features is fun, but the combined affect of their dynamic operation is where the results are seen in the target. The operation of the firearm as a whole, in the hands of the user, is far more significant than a casual discussion of what individual feature might be better.

April 30, 2012, 11:02 AM
im designing a rifle of my own right now in 3D... uses a long piece of steel tubing that makes up the upper receiver, forearm, and part of the stock... so in the end itll probably end up looking like a scaled down m82 barrett...

currently, im stuck on a couple features.. im not sure if i want to make it top eject, or side... my goal is to make it ambidextrous... one idea i had was to cut an ejection port in each side... then when it ejects the round, the other side will be open to to help blow out fouling, and possibly debris... my other idea was to make it top eject...

this design as it stands is a .308 semi auto rifle, lever-delayed blowback, but the lever itself is under spring tension to delay blowback, this allows the lever-delayed system to be adjustable...

however, springs do break, and should this one break, the lever wont work, and should that happen it wont lock up... so with this in mind im currently working on a failsafe, and the way im going to do this is the other side of the spring will press on a lever that holds open a firing-pin block... if spring tension is for some reason lost, the firing pin block engages and prevents the rifle from being fired...

chances of the spring itself breaking is incredibly slim, like winning a lottery slim... but doesnt hurt to plan ahead for that possibility and find a way for it to fail safely...

if made to be top eject, my idea is to cut slits in the side of the tubing for the rails, and use T shape pieces of steel slid into those cuts, and welded from the outside after the sides of the T are bent around teh receiver... this does two things, gives me rails, and greatly increases the strength and rigidity of the receiver

since the receiver is mostly a piece of tubing, no guide rod is needed, the recoil spring will just equal the inside diameter of the tubing... and the front trunnion itself will have a piece extended below for the fire control group to be pinned on to..

at this point im just going to use a fire control group that can be purchased online, like an AR-10 group, or tapco AK trigger setup

and as of yet, i have decided where the magazines will come from, i really like the AK-style rock-on magazines, so possibly saiga .308 mags

havent decided yet if the magwell will be part of the upper, or part of the lower


id love to hear comments and questions about this idea, fun to design things in 3D and discuss them

April 30, 2012, 11:26 AM
i really like the AR-15s barrel setup.. how they attach that barrel is very nice... ive considered using a similar means... would be cool to use AR-15 / AR-10 barrels.. i may have to consider incorperating that into my design...

ive also thought about eliminating the barrel shroud extending from the receiver, and just extend and thread the trunnion beyong the receiver, and get another piece of tube steel to thread.. then just screw it over the trunnion for a completely free-floating forearm, with the option of switching out forearms as well.... i was already going to use AK style pistol grips, since theyd mount more easily to the bottom of the trigger group than the AR-style

April 30, 2012, 02:40 PM
I'm glad you're thinking outside the streamlined box, and giving thought to a simple chassis. I am very interested in various methods of delaying the action. Everything for rifles is going the way of the rotating bolt, whether for accuracy or ease of manufacture.

Lever-delayed is very neat and I often wondered why it's not in more small arms than the FAMAS. I also like the tilting-block designs, like the VZ-58. I don't really have much technical info to add tho, I know many on here a far more knowlegeable than me.

I agree with Henschman in post #6 and would like to add modular design and easy disassembly like an AR.

Rail Driver
April 30, 2012, 02:46 PM
Keep in mind that springs are considered "consumables" - they're GOING to break. Some springs are viable for thousands of cycles, and some springs are viable for hundreds of thousands of cycles, but eventually they all weaken and break.

April 30, 2012, 02:55 PM
yeah rail driver, which is why im finding a need to develop a means for it to fail safely if a spring fails... maybe add redundancy with two levers, two springs, and have it set so if one fails, the other is still good enough to allow function...

but i was going to have the spring, when the lever is installed on the bolt add tension to a firing pin block.. once the spring breaks, tensions gone, firing pin block locks the pin in place...

HK91 uses rollers instead of levers, and i believe their rollers are spring loaded too, but they do use two of them... so it would be similar to an HK rifles delayed system, just with levers that hook into a groove inside the trunnion


im also going to work on a gas powered rifle when this is finished... umm, actually, the only other rifle im aware of with the action im looking at is the old STG 44...

ive put a lot of thought into the type of gas system i would want most, and come to the conclusion that rotating bolts tend to be stronger, more reliable, and less likely to jam from dirt or debris, so id go tilting bolt.... also, i like the tradeoff the long-stroke piston offers with the piston riding the bolt carrier all the way back... if something gets in the way of the carrier on a DI or short stroke system itll fail to extract, and jam

April 30, 2012, 02:56 PM
Yes, definitely a modular upper/lower design, and I forgot to add a left side charging handle.

April 30, 2012, 03:07 PM
what are you definitions of modular? what would your requirements be for a modular design?...

henschman, with my design i intend to have a charging handle that can be easily removed and switched to either side... i wont design something thats not ambidextrous

April 30, 2012, 03:52 PM
What about downward ejection and top-mounted magazine? Gravity assisted feed is pretty reliable , as witnessed by the Owen Gun, Lewis Gun, DP-28, etc. And downward ejection makes it a lot easier to swap right or left handed. In messing around with AR and M1A designs, I'm discovering that the bottom-up magazine feeding often presents the most reliability problems.

Rail Driver
April 30, 2012, 03:55 PM
What about downward ejection and top-mounted magazine? Gravity assisted feed is pretty reliable , as witnessed by the Owen Gun, Lewis Gun, DP-28, etc. And downward ejection makes it a lot easier to swap right or left handed. In messing around with AR and M1A designs, I'm discovering that the bottom-up magazine feeding often presents the most reliability problems.
Top mounting a magazine, unless it's spring driven and horizontal like the P90 mags, is going to seriously limit the sighting/aiming possibilities.

April 30, 2012, 04:06 PM
It's a challenge, for sure. But it can be done. These were after all some of the most popular and successful small arms ever fielded. We're just not used to top mounted mags these days.

April 30, 2012, 05:32 PM
ive put a lot of thought into the type of gas system i would want most, and come to the conclusion that rotating bolts tend to be stronger, more reliable, and less likely to jam from dirt or debris, so id go tilting bolt....

Huh? You're postulating all these advantages for rotating bolts and then decide on tilting bolt?

The main advantage of rotating bolts is that they offer very good primary extraction. Secondary, you can reduce the size of the barrel extension by using a front locking rotary bolt. A rear locking tilting bolt is going to require more steel as the locking area is further away from the chamber.

Not a lot of new delayed blowback operated weapons have been developed since the 60's. Problems include sensativity to variations in ammo and a tendency to mangle brass as they all allow the bolt to move while cartridge pressure is very high. Delayed blowback weapons are also going to require either a fluted chamber or lubricated cartridges to keep from tearing the cartridge apart.

If I were designing a rifle class weapon I'd stick with gas operation with a adjustable regulator (like the FAL) and a rotating bolt.


April 30, 2012, 05:38 PM
a top mounted magazine could work... but it couldnt be a typical box magazine, that just gets in the way.. perhaps a helical magazine would work.. especially if its mounted on the top of where the buttstock would be, sights wouldnt be too bad either... and i guess someone could always scale up a P90 mag and find a way to use it... but ultimately helical will probably hold more ammo

it just seems so much easier to eject out the top... it was used on rifles all the time way... thompson i believed was top eject, russian PPSH was, MP40 was angled at the top, garand is sort of top eject, various lever actions were... as long as you didnt have some 24 inch long scope you had to mount i doubt youd risk any rounds hitting your optics...

side ejection is a must with modern gas-operated rifles since the gas pistons usually in the way... but i guesss you might be able to get away with top-ejecting a short-stroke or DI system...

i guess the key that should be focused on is comfortable magazine changes.. not having to reach into any akward position to change it, reliable feeding of course, and secure seating...

one reason i like the AK style magazines is you hook them in and rock them back, they seem to seat more securely, where with the type you pop into the magwell ive noticed sometimes you have to smack them to get them all the way in...however, magazines that drop right out with the push of a button or lever with your index finger is certainly useful for a fast reload

more tradeoffs i guess

April 30, 2012, 05:43 PM
i already have one gas operating rotating bolt that ive designed, theres not much to them... with the rotating bolt design i had... i designed it in a way that you could remove the bolt from the carrier, turn it upside down, and re-insert it, causing it to eject from the opposite side of the rifle... then i had an ejection port on each side.. with the bolt closed, the bolt block anything from getting inside, and once opened to eject a cartridge, the other port aided in more airflow for cooling, but had a dust cover you could close for dirty, dusty situations

Rail Driver
April 30, 2012, 05:49 PM
i already have one gas operating rotating bolt that ive designed, theres not much to them... with the rotating bolt design i had... i designed it in a way that you could remove the bolt from the carrier, turn it upside down, and re-insert it, causing it to eject from the opposite side of the rifle... then i had an ejection port on each side.. with the bolt closed, the bolt block anything from getting inside, and once opened to eject a cartridge, the other port aided in more airflow for cooling, but had a dust cover you could close for dirty, dusty situations
I'm having trouble envisioning this in my head - have you actually built a working prototype of this or is it just a 3d model/blueprint?

April 30, 2012, 05:56 PM
By "modular," I just mean that the upper can be quickly and easily separated from the lower.

April 30, 2012, 07:17 PM
no prototypes yet, just 3D design and simulations...

and to hesch... isnt a seperate receiver/trigger group pretty standard on most rifles?.. heck even the garands trigger group/magazine seperated

its so hard to say how well a lever-delayed blowback will work, since i can only think of one example out there.. the french FAMAS, other than that, roller delayed on the HK and a couple pistols seem to build an incredibly reliable, very accurate rifle... but it is true the chamber does need to be fluted for reliability, and partial extraction while under pressure could damage a case..

im also working on another idea that uses a floating chamber which doesnt have those issues... the way this works, is theres a breachplug in the barrel extension that holds the cartridge, when the round is fired, this extension is pushed back like 1/10th of an inch then stops... the momentum causes the bolt to continue moving backwards to extract the round and cycle a new one working like a short-stroke piston, with the chamber itself acting as the piston... and since the chamber only moves 1/10th of an inch, it remains within the barrel extension and the gasses remain in the barrel

April 30, 2012, 09:03 PM

April 30, 2012, 09:34 PM
im going to finish up this lever-delayed blowback design and then work on the floating chamber design a bit, i could maybe render some of the final products if anyone wants to see a photo of what it may look like?

April 30, 2012, 09:49 PM
Why does it have to eject anything at all?

About twenty years ago a working full auto was designed to simply shove the empty case ahead of the next, becoming the projectile that was powered by the one behind. Rather massive hollow point, but that was the first gen - just fire "blanks" and keep shoving another loaded case into the barrel.

By the way, what's the range and target of this mythical gun? Those parameters have a lot to do with the ballistic requirements, and those drive a lot of the design decisions.

April 30, 2012, 09:54 PM
Careful Jason, if some of these ideas are patentable, some schmo or corporation will snap them up if you get too specific...

I think the firearms industry is worse about this than any other. If you think any of your ideas are "novel" and show any promise as a viable design, you should think about getting at least a provisional patent. There's no profit in just giving your ideas away...

I'm pretty sure every one of today's "big players" got there by ripping off and undercutting each other prior to a big war's contracts :((there's no "for shame" smilie)

Your floating chamber idea almost sounds like short recoil; the chamber is like the pistol barrel, and the bolt is like the slide. If you could ensure the bullet can jump to the barrel from the chamber piece before it begins to move, you'd end up with a very compact action. The trick would be to keep the bolt/chamber together long enough to ensure ambient chamber pressure. It would be tough to keep the two together under the stress of anything larger than a pistol cartridge without a locking mechanism, which would turn the design into a sort of delayed blowback, I suppose. A delayed locking device would allow you to use higher/longer pressure spike rounds, like intermediate rifle calibers. It's a cool concept, sounds very simple and compact, would probably make for a good subgun.

But unless you are chambering your action for an intermediate cartridge, delayed blowback may be difficult. The more powerful the round, the greater the delay needed to get safe pressures. Since delayed blowback locks typically depend on bolt mass and mechanical disadvantage, I always either end up with a really heavy gun, or extreme ammo sensitivity (easy short-cycles or case-destruction outside of "ideal" chamber pressures) when I run the math.

In my design musings I always found it more convenient to utilize tapped barrel gas, since it can be regulated by orifices unlike chamber gas in a blowback action. But if the rounds you are firing are smaller (I think there's a ratio out there for bullet/bolt mass) there is hardly a more efficient lock mechanism than delayed blowback or short recoil.

I'm glad there are folks out there still interested in innovating new concepts for these ancient weapons. Gun actions make for great thought experiments, don't they? Seems like everyone and their brother has been making the same half-dozen guns lately. People even identify their firearms by the guns they were copied from (AR, AK, 1911, etc). Just like good art, a good design shouldn't be purely derivative.


April 30, 2012, 09:54 PM
The HK delay system actually uses a wedge piece attached to the bolt carrier to cause lock-up, by means of the bolt carrier moving forward relative to the bolt head under both recoil spring pressure and BC momentum.

I would try to design some sort of similar camming action into your lever, as opposed to a (i'm guessing fairly small) spring. Small, high tension springs tend to fatigue fairly quickly, in my experience. I think by making it a positive mechanical actuation, you'll make it more durable and reliable...

April 30, 2012, 11:41 PM
where would the tension on the lever be gained from with a cam action?... hmm, wonder if theres some way to use pressure from the mainspring to apply tension to the levers?

also.. lever-delayed blowback, and floating chamber designs are already out there... nothing for me to steal, just adapting whats already there at this point.. if i come up with anything particularly useful i promise no one would know about it

ive never heard of pushing an expect casing out the front... it just seems difficult to do...

i guess the best way to not have to eject something is to somehow encase the powder into the cartridge base like the old volcanic pistol did.. but energy would be so small...

i wonder if its possibly to develope some kind of perishable casing... maybe.... i know old muzzleloaders used nitrated paper to hold powder and a bullet for quick reloading.. if it was some how possible to stiffen the the nitrated paper so it remained rigid in a way that it would completely burn up upon firing.. would just need a chamber that was sealed from pressure.. and for safety purposes i would only cycle something like this via a gas piston and a rotating bolt...

umm, certain pine resins are very high in heptane, which is highly flammable, can be used as fuel.. with these sticky resins one could make a glue... possibly using this glue to coat and stiffen a nitrated paper cartridge could possibly create a consumable paper cartrdge that might just be stiff enough to handle being stuffed in a magazine, and fired from a rifle

anyone have advice on an inexpensive rifle easy to work on and not a major loss if one of these ideas were to fail? (fired remotely of course).. or it might be better to come up with a single shot platform with a thread-on breach for testing... like a threaded rifle barrel.. load a cartridge, then screw on a threaded steel cap with some remote means to fire it for testing experimental and wildcat cartridges

Rail Driver
April 30, 2012, 11:49 PM
If you're looking for a inexpensive, but robust rifle to test theories out with, get a case of Mosin/Nagant rifles. They don't get much more robust or cheap than that.

April 30, 2012, 11:51 PM
one thing i made for a black powder firearm.. was i made the black powder by grinding all components into a fine powder, mixing them to the proper 75/15/10 ratio with a bit of distilled water... moulded it into a tube, and it remained rigid when solidified... i believe they do the same thing with smokeless powder (nitrocellulose) to make caseless ammunition... its basically like mixing concrete and letting it dry solid.. and can be moulded to hole a bullet and primer

question is.. what happens to the primer when its fired? does it just fall out the barrel? or drop out of the rifle when the actions cycled?.. is the primer consumable as well? i didnt have to worry about that in a muzzleloader

April 30, 2012, 11:53 PM
rail... i think ill just machine a breach section for a standard remington 700 barrel.. just a piece that can be threaded over the barrel itself with a some remote-means of firing it.. i just wouldnt have any need for a stock, sights, trigger group, etc as it would all be clamped down to a bench or table

May 1, 2012, 06:48 AM
What is the purpose of the self loading rifle under discussion?

Direct blowback operation is only suitable for pistol caliber cartridges. Recoil operation is generally considered obsolete as far as shoulder fired automatic weapons go, but could be an option for a heavy caliber such as .50 BMG. Gas operation is probably the most suitable for a centerfire shoulder fired semiautomatic rifle.

Direct impingement is suitable for a "sniper" or designated marksmen's rifle. A gas piston (either type) is probably better for a general issue rifle, although this is open to argument.

In practice, delayed blowback actions tend to be fussier about ammo. For a military, which might only supply one bullet weight, this isn't an issue. On the other hand, a civilian reloader would be infuriated by an action that would only function with a limited variety of bullet weights and that might destroy brass.

Magazine type depends on the purpose of the rifle. A fixed box magazine would be a bad choice for a light machinegun. Belt feed would be a poor choice for a sniper rifle.

Furniture depends purpose.

Caliber depends on purpose.

Although you sorely neglected to mention it, bullpup or not is another contention to consider. Once again, it depends on the purpose of the proposed rifle.

Being a monetarily impaired individual, the perfect semiautomatic rifle if I were to design it, would be something like the top half of a Leader Arms carbine (simplified AR-18) combined with a plastic lower such as a PCF or Cav Arms.

May 1, 2012, 09:54 AM
purpose of the discussion is to discuss all options and design features of whatever youd like to discuss

May 1, 2012, 06:03 PM
anything else anyone would like to discuss?

May 1, 2012, 07:40 PM
i guess the best way to not have to eject something is to somehow encase the powder into the cartridge base like the old volcanic pistol did.. but energy would be so small...

i wonder if its possibly to develope some kind of perishable casing... maybe....

Ever heard of re-inventing the wheel? A little research will save you an immense amount of time - you may want to look into caseless ammo and combustible cartridge cases - both have been around for a long time in modern forms.

Hint- take a look at an H&K G11, or a M829 120mm cartridge.

May 1, 2012, 08:22 PM
HK G11 uses a powder mixture mixed and packed into a mould to dry into shape.. but is quite brittle, paper cartridges were used in civil war era muzzleloaders...

for caseless ammo.. why dont they use both?.. start with the solid propellant wrapped in a nitrated paper held together with some type of combustable resin.. would be durable enough to cycle through magazines, be tossed around a bit... and be entirely consumable.. thats what i would do if i was going caseless.. but its certainly a touchy technology to get into, wasnt even me who brought it up though

May 1, 2012, 09:23 PM
How come nobody uses a gas retarded system on a carbine, similar to the HK P7 pistol? You could mount the piston above the barrel to keep the hanguards from getting obscenely hot.

I would like to see a carbine that uses a (mostly) vertical block that delays opening, then is cammed out of place by raceways on an op rod/bolt carrier.

May 1, 2012, 09:46 PM
do you mean like a falling block in an 1885 single shot, but semi automatic?

May 2, 2012, 04:37 AM
I mean a a semi-auto carbine with a bolt locking block, roughly borrowing the idea from an AVS-36.

My thinking was that this could be rearranged somehow, instead of between the magazine and breech face. The locking block could be U-shaped and fit around the barrel; and an op rod could unlock it. If nothing else, it could be there for mechanical disadvantage.

May 2, 2012, 09:42 AM
that reminds me of what john browning did on the 1886 lever action.. used vertically moving lugs like that to lock the action... that would be very easy to work out though... just have the bolt carrier push it down by running over the top of it with an angled section to push it down, and then continue pulling the bolt to open it...

i doubt it can be moved rearward though, it would have to lock the bolt and in order for it to lock the bolt it would have to extend backwards beyond the magazine which also means a longer bolt carrier and more weight.. probably better off with it in front, but somehow out of the way, like off to the sides....

the russians scrapped this idea because it was pretty lousy in practice

hmm.. does a carrier actually open the lug on that, or does the gas system itself unlock it and allow the bolt to be pushed back from gasses in the chamber?

May 2, 2012, 10:29 AM
Guns are simple machines. The FCG is the most complicated thing on most firearms, and even that can be understood by the average user if they take some time and study a decent diagram.

With that in mind, what does it really matter what kind of operation a gun uses? They all have their trade-offs, and as long as you maintain them and use the right kind of ammo they pretty much all work.

May 2, 2012, 11:10 AM
Guns perform a simple function, but the few parts that comprise them have suprisingly complicated interactions.

I like the idea of a vertical drop locking device, seems like it could be scaled to hold back a wide variety of cartridges since the lock itself doesn't depend on the cartridge's pressure level or bullet momentum. However, since the falling element is outside the bolt/chamber assemblies (unlike rotary locking lugs) the reciever will have to be beefier where it braces the falling block, right? Seems it could make the gun heavier if not done right. I wonder if it might be safer though, since a firing pin safety based on the position of the block would be a guarantee of full lockup before ignition.


May 2, 2012, 11:42 AM
barnbwt.. are you saying have the falling block portion with a firing pin hole in it so that unless that block is fully locked, the firing pin wont move?... or if it was partially closed, there might be enough force in the firing pin to close it and still ignite the round, or otherwise not fire at all?.. that does seem pretty safe....

would this design be gas operated with a bolt carrier acted upon by gas forces, in which case it can slide under an angled portion of the block and lift it, or push it down before dragging the bolt along,

or would this be a type of gas-delayed blowback system that uses gasses in another chamber to push the block away, allowing the bolt and cartridge to blow back without the partial extraction before cycling?

May 2, 2012, 12:33 PM
Like any bolt lockup, energy from gas or recoil/blowback can unlock the mechamism. But since the force needed to disengage a falling block is totally perpindicular to the line of action of recoil, it could remain locked without any other consideration as long as it takes to get safe pressures (you can reload a lever action as slow as you want) which gives you more flexibility when it comes to timing the unlock/eject sequence. I've always wondered if anyone ever tried unlatching/cycling a bolt with the return stroke of the piston, since pressures have to drop before it can move forward.

As far as the pin safety, I was just saying it would be easy to rig something up to make the latch itself double as the trigger disconnector, which seems like it would be more Murphy's Law resistant. What you described seems like it would work, you just want to be sure that block doesn't try to fall while the pins in it.

I wonder if you build everything into the block like we do with the bolt nowadays, and use the bolt carrier to rip out the round once the bolt/block drops clear. Sort of like a miniature howitzer I suppose.


May 2, 2012, 01:16 PM
thats starting to sound overly complex for a design, because if everythings in the locking block then its difficult to recock the hammer, eject the catridge, load a new one

May 2, 2012, 09:12 PM
any of you see the gas delayed blowback systems such as those in the H&K P7 i believe it was?.. ive never seen one of these personally... but apparently theres a second chamber near the barrel... when the guns fired, this chamber gets pressurized and pushes agaisnt the piston, which has a spring against it.. as long as theres a certain amount of pressure in this chamber, the bolt wont move.. but as soon as it drops the spring pushes the piston forward again and opens the action to cycle...

am i understanding the way this action functions properly?.. or am i missing something?

May 2, 2012, 09:59 PM
That HK is a clever little thing, from a number of moving parts perspective. It's really about as simple as a direct blowback.

Given the power available from a gas tap, I think this setup could be strong enough to delay a rifle cartridge at peak pressures, but I'm not sure if rifle pressures drop fast enough to work well safely. It seems with this gun that once the pressure gets low enough that the spring can over come it, you would want any remaining pressure to be gone immediately.

That little remaining pressure is what has to extract the casing and move the heavy bolt, I'm not sure if a near-ambient residual pressure would be strong enough. You wouldn't want that cartridge coming out of battery with even hundreds of psi still left in it, but that may be what it takes for Force=Pressure*Area to be high enough to reliably cycle a rifle action. I wonder if that pistol may be simply a slightly delayed blowback in reality.

Unless you can find a way to quickly vent the chamber once it picks up momentum (but before it vents out the ejection port), I think you'd still need a postive mechanical delay for something more powerful than a mid-size pistol cartridge. If you allow the barrel-piston to shift forward a bit under pressure , you could have it charge a spring that would fling it back more assertively once pressure drops enough.


May 2, 2012, 10:53 PM
are you saying the gas pushes the piston forward, and somehow that locks with a carrier that once the gas is gone moves back from spring pressure.. then disconnects as the mainspring returns the bolt forward?... seems like a gas system that operates on the return stroke

May 3, 2012, 09:43 AM
Pretty much :)

I just don't think a delayed blowback can be made to function with high pressure rifle cartridges, at least that's the cureent state of things. By using the gas delay to carry the bulk of bolt thrust load at peak pressure, I imagine the gas operated lock wouldn't need to be as over built, though.

I guess the solution to a delayed blowback rifle may be a combination of delaying/locking methods, which doesn't necessarily over complicate the design.


May 3, 2012, 10:50 AM
you dont think a high powered rifle can be made to function with delayed blowback?.. how about the H&K G3 / CETME rifle? roller delayed blowback and been in reliable, durable service since the 50s in the form of a .308 assault rifle, a 5.56 assault rifle, a sub MOA sniper rifle, a belt fed LMG, as well as a submachine gun...

also the french FAMAS rifle is delayed blowback

May 3, 2012, 11:07 AM
Before going off and creating a design I recommend you try to find as many firearm design books that you can. This is my list, of the ones I have been able to acquire. This will really help you in your search for desirable paths to go.

1.“Technical Notes, Small Arms Design”, Author: John G. Rocha , available from Armalite (800) 336-0184, stock number NA1085 $12.50 . Maybe be out of print, cannot find it on This soft cover pamphlet is a copy of the course material handout to a firearms class taught at Rock Island in the 60’s. Very interesting, a good number of formulas, but still very readable.

2. Brassey’s Essential Guide to Military Small Arms, Design Principles and Operating Method, Author Allsp and Popelinsky, Brassey’s Inc, 1997 Out of print. This starts off simple and ends up very technical. This is a serious book and the final sections really require education in math, science, or engineering. Currently on Amazon for $600.00!

3. The Machine Gun, Volume IV, parts X & XI, LTC George Chinn, pub 1955. Out of print. This book should be the absolute first book to buy for someone who is interested in the principles of automatic weapon design. Really an excellent statement of principles. It is a comment on the general state of technical ignorance in our society that this book is extremely rare, but the general public is not that much interested in it. A Gun Show book dealer told me more people wanted the volumes with the pretty pictures of old guns!

4. The Bolt Action by Stuart Ottenson. First edition by Winchester Press 1976. Ottesnon later added a Volume II which came out in a two volume edition by Wolfe Publishing in 1985. These books are very non mathematical for a general audience, but the principles, particularly expounded in Vol 1 on the Mauser 98 are, in my opinion, fundamental to the understanding of bolt action design.

5. AMCP 706-260. Engineering Design Handbook: Automatic Weapons. Out of print. The most technical and mathematical design book I have found to date. Assumes a high level of knowledge in firearms design, mathematics, and Mechanical Engineering. A technical degree, preferably in Mechanical Engineering is really needed to attempt to understand the presented material. This was created in the early 60’s, and reflects the designs, and the design knowledge of the day.

6. AMCP 706-252 Engineering Design Handbook: Gun Tubes. Out of print. Very interesting, not limited to small arms.

AMCP stands for Army Material Command Pamphlet. There were about one hundred AMCP Pamphlets covering information ranging from Statistics to Automotive Design. A copy of AMCP 706-260 and other out of print AMCP pamphlets can be ordered from NTIS at These are not cheap, they want $45.00 to $150.00 for some of them.

7. Small Arms & Cannon, Smith and Haslam, RMC of Science, Shrivenham UK, 1st Edition, 1982, Brassey's Publishers LTD. Excellent read, look on Amazon.

8. Small Arms, Volume 6 of Brassey’s Land Warfare into the 21st Century, copyright 1999. Brassey’s UK, Authors D. F. Allsop and MA Toomey. Out of print. Excellent book, an expansion of reference 2 with more technical data added. Currently on Amazon for $120.00!

9. Ballistics, Theory and Design of Guns and Ammunition. CRC press, 2008, Authors Donald E. Carlucci and Sidney S Jacobson. This book is highly mathematical, primarily artillery related. A considerable advancement on interior, exterior, and terminal effects from earlier references.

Firearms design books are so rare because the market is very limited. I would suggest to anyone who has a technical background, and is interested in firearms design, to acquire those books in print. Because once they are out of print, you may never find one, or you have to pay the sky high prices on Amazon.

May 3, 2012, 11:23 AM
yeah.... wow, $600 for a book... i dont even think i paid that for all of my mechanical engineering books, and i got a degree with that... for $600 i better get something

May 3, 2012, 11:31 AM
anyway.. im continuing this thread on thefiringline for now... so instead of replying here.. just go there and reply

May 3, 2012, 01:01 PM
i dont even think i paid that for all of my mechanical engineering books, and i got a degree with that... for $600 i better get something

Really? My senior year books cost more than that, in 1997.

May 3, 2012, 10:05 PM
My senior physics books cost more than that alone, and half of them were used! AND that was a decade before Owen.
I detect an absence of factual accuracy (or memory) that brings much of what was said into question.

Art Eatman
May 3, 2012, 10:22 PM
Since the OP has gone away and will post here no more, he says, there's little point in continuing this thread...

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