piston or gas


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gator-1
February 28, 2010, 02:12 AM
i was wondering what the advantage and drawbacks was to the piston and the gas operated AR rifles. RRA seems to speak highly of the piston and is having a sale? on their operator line of ARs. Thanks for any info folks

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mnrivrat
February 28, 2010, 02:48 AM
Both systems are gas operated. The original style AR15 system has a gas tube that runs rearward from the front sight area into the receiver and acts directly onto the bolt key.

In the piston system the gas operates a piston near the front sight that drives a rod ,that goes rearward into the receiver, and acts on the bolt key.

Two advantages of the piston system are that it is adjustable for different power levels, and the second is that it keeps the gas/residue out of the receiver which helps keep the gun functioning longer between cleanings.

briansmithwins
February 28, 2010, 10:06 AM
Both have gas pistons. In the original design the bolt and bolt carrier form the gas piston. In the 'piston' designs the gas piston is up by the front sight and a rod is used to transfer the energy.

The advantage of the original design is that 10s of millions have been made. It has weak points but those are pretty well known. With retrofit designs you don't have a large installed base and you're locked into a proprietary design.

I figure if I want a military pattern rifle I want it to be as close to issued as possible. BSW

hk lover
February 28, 2010, 10:45 AM
I've been reading of some problems on piston operated systems of "carrier tilt".
It seems that a piston driven rifle may indeed be cleaner and cooler, but it's hard to argue the point that properly maintained the direct impengment[spelling] is a fine weapon that has worked many years under harder use than a civillian would encounter.YMMV

Zerodefect
February 28, 2010, 10:46 AM
The air pressure in the Ar's carrier blows it straight back. The piston conversions push on the top of the carrier. This causes incresed friction as the carrier twists on its rails. This also can slam the carrier into the buffer tube where it starts diging a nasty hole in the buffer tube. Piston AR's get red hot where the piston is on the barrel. Piston Ar's are also more nose heavy an a bit slower to swing around.

Piston conversion AR's are nowhere near as reliable as the GOOD teir 1 AR's yet.
There alot of bugs people have had to t-shoot out of thier piston AR's. If your good at that go for it. But I'd recommend buying a piston gun that was desighned from the ground up to be a piston gun.

You can dremel then polish a ramp on the buffer tube where you see wear. You can also bevel and polish the back of the carrier. There is a new buffer someone on ar15/.com is selling that has an extention that keys into the carrier reducing the carrier tilt but transmits friction inside the buffer tube. So that needs to be kept wet. Also that goofy buffer won't let you pull one pin to remove the carrier, you have to pull both pins and split the gun.

Better off with a Robinson XCR ( my fav piston rifle), FN Scar, FN FS2000, Bushmaster Garden Weasel ($2500!), Sig 556

Ar's were meant to be DI, no real world advantage swapping to a piston.

Quentin
February 28, 2010, 11:23 AM
I agree with the last three replies, why go with a proprietary system that introduces new problems (explained above). And there's the worry that the maker of the unique system you bought will cease production of it down the road, leaving you with an orphan. Nothing seriously wrong with DI so stick with it unless you really want to play with something new.

Roadkill
February 28, 2010, 11:38 AM
I'll toss this in just cause I can - I spent over a year and God knows how many hours getting a .223 FAL to work. Without getting in all the details the overall problem was that the .223 round did not put enough gas pressure up into the gas block to get the piston to overcome resistance from the piston spring, hammer spring, return mainspring, weight of bolt, ejector, and resistance/drag on the rails. It takes a near max load of 4895 with a 77g bullet after I reduced resistance on all the springs and polished every contact point between bolt and rails for it to run and I nearly doubled the size of the gas opening in the barrel. The 4198 powder with either 62 or 55g bullets I use in my five other .223 guns barely unlock the lugs on the FAL.

Boba Fett
February 28, 2010, 12:18 PM
Watch nutnfancy's video comparing the piston vs gas systems:

http://www.youtube.com/watch?v=6auXTiqNtEo

Very good info presented in a neutral light.


Personally, I'm waiting on the piston guns.

I'd like to see more time behind the piston system in the AR platform before I buy one. More history = a better idea of the failures and weak points of the system. We already know what they are in the DI system and can take steps to shore them up and maintain them.

I'd also like to see a standardized piston system for the AR. Seems like every company comes out with their own piston design. Part of what is so good about an AR is the general ability to find inexpensive universal replacement parts.

winknplink
February 28, 2010, 02:16 PM
IMO, you own DI AR's for the same reason you own a 1911 and a glock17...b/c there are literally millions of them out there. That means parts and ammo are affordable (relatively speaking), available and more abundant than anything else...which is especially handy in a SHTF scenario.

But, that could just be my admiration for Jeff Cooper speaking...

Jaws
February 28, 2010, 02:56 PM
The direct impingement AR is that one time experiment, that ended up being the main rifle for a reason or another. I doubt you'll ever see another DI general issue rifle adopted ever.

But the AR15 was designed as DI rifle from the start. Adding a piston, depending on how well the design changes are made, may introduce other problems not present in the original rifle, so the advantages could be negated by new, unsuspected problems.

Hatterasguy
February 28, 2010, 05:04 PM
I think if you want an AR get a DI gun, thats how they were built and for 99.9% of users they are 100% reliable.

If you want a piston carbine in 5.56 get one that was built as a piston gun from the ground up.

The Europeans have made some very, very good rifles that fit this catagory. The G36, Sig5XX series, FNC come to mind.

The_Hammer_Man
February 28, 2010, 05:21 PM
http://www.thehighroad.org/showthread.php?t=502559

A previous thread that covers this question pretty extensively by myself and other knowledgable types.

The too piston or not to piston choice is much debated with LOTS of folks on both sides. It gets pretty heated at times too. The thing to remember is that while the DI system is "tried and true" it has it's faults. Same with the piston drive system of operation.

The biggest single advantage to piston driven rifles is reduced receiver/BCG wear because less unburnt powder and other barrel gas contaminants do not get cycled through the receiver like they do with DI rifles.

snakyjake
March 1, 2010, 12:59 AM
Piston systems are great if you don't clean. I have some serious doubts a piston system designed into the AR15. I don't like hearing about potential piston problems on the AR15. I don't want to spend my money to be an early technology adopter. If I want a piston system, rather have a system designed for it. Give it a few years, let the bugs get ironed out. Let the military and law enforcement agencies work the bugs out. When they decide what works, then I'll buy.

SHvar
March 1, 2010, 01:50 AM
Gas piston AR rumor corrections...
Not all gas piston AR designs have carrier tilt, in fact very few cases of carrier tilt on a few models have actually occured, but just like anything else, rumors fly faster when they are juicier. Keep in mind I bought a piston AR that has a gas piston design built to the rifle from the tried and true POF design, not a retrofit kit.
Second, retrofit piston ARs have the factory bolt carrier adapted, but some come with a carrier that is built just for that purpose (heavier in the back, shaped a bit different, and the point where the op rod pushes on the carrier is a solid machined part of the carrier, not bolted there).
Piston ARs do get hot in the front sight/piston assembly area (so do DI models when fired alot), but they cool down fast.
Keep in mind that they are ALOT cooler in the upper reciever/bolt/carrier area. In fact a piston AR can be fired rapidly for hundreds of rds, then the bolt/and carrier can be held in your bare hand, it wont even be warm.
The bolt carrier in a piston AR stays wet with oil, and very clean regardless of how many rds you fire through it.
Now to address the subject of the increased weight issue. This was covered by a few of us who actually own piston ARs. Below is a list for reference of the actual weights of comparable 16 inch, 20 inch, and 24 inch AR models from one manufacturer alone, this should put an end to the front heavy rumors.
Keep in mind that the gas piston design (M4) I have weighs 4.48 ounces more than a standard 16 inch M4, to add to its weight difference it has much larger double heat shielded handguards, and 3 solid rail sections attached to the front of those handguards. I believe that someone here weighed the gas piston assembly to a whole 3.5 ounces at most.
Remember this, when you see these AR carbines with quadrails, the weight difference between a DI AR with a quadrail and with plastic handguards is over a pound, a 20 inch rifle would be heavier with a quadrail yet.

Gas piston M4 with POF gas piston design, 6.5lbs or 6lbs 8 ounces.
Standard DI M4 with 16 inch barrel, 6.22 lbs or 6lbs 3.52 ounces.
6.8mm DI M4, 16 inch barrel, 6.5lbs.
DI M4 patrolmans carbine, 16 inch barrel, 6.35lbs, or 6lbs 5.6 ounces.
16 inch carbine Hbar, 7.28 lbs, or 7lbs 4.48 ounces (flattop model, A2 is 6.93lbs).
11.5 inch entry carbine, 6.81 lbs, or 6lbs 12.96 ounces (flattop A3 model, A2 is a bit lighter).
16 inch midlength rifle, 7.44lbs, or 7lbs 7.04 ounces.
Carbon 15 flattop rifle, 5.77lbs, or 5lbs 12.32 ounces.
20 inch (flattop) A3 rifle, 8.78 lbs, or 8lbs 12.48 ounces.
20 inch Hbar, 9.6lbs, or 9lbs 9.6 ounces (without buttstock insert, with insert 13.6 lbs).
24 inch stainles steel varmit AR rifle, 8.84lbs, or 8lbs 13.44 ounces.
Gas piston ARs have adjustable gas systems in some cases, they can be adusted for stronger recoil or lighter, for use with a supressor, or without.
Why did the gas piston design pass the toughest tests our special forces (H&K 416) could throw at them if they are so "untested", and have all of these problems that are mentioned by those who have never owned one, let alone shot one? Why was the gas piston design bought to be used in the desert (Iraq, and Afganistan) by our special forces units, better yet it was these soldiers and sailors that helped to design the gas piston replacement rifle until the SCAR was purchased.
The primary differences felt with DI and gas piston ARs when firing, the gas piston model has a higher percieved recoil from the movement of the gas piston assembly, is louder, and takes a few rds getting used to when firing accurately when your used to the DI model. Id venture to guess that most soldiers would be less accurate with a gas piston rifle over a DI rifle, but thats the DI rifles advantage. With practice there is no big difference among many shooters.
Gas piston ARs clean in a hurry, the longest part of the job is cleaning the barrel (easier than a DI rifle), next the gas piston assembly (a few minutes), the rest takes a few minutes to wipe off and re-oil.
Depends what you are looking for, if you want a gas piston or DI AR, chose which you want, weigh the real differences, not rumors, or half truths to decide. If you buy a gas piston AR, buy one that has the gas piston design built and assembled by the manufacturer on the rifle with a warrantee, not a retrofit kit. The original designs are much better designed, and are much more substantial built.
Heck, buy one of each, their both fun to shoot.
Heres the big POF design that weighs a few ounces more than a small gas tube.
http://i193.photobucket.com/albums/z281/SHvar/Picture095.jpg
http://i193.photobucket.com/albums/z281/SHvar/Picture100.jpg
Im sure 3 of these rails make up a few ounces of that 4.48 ounce difference..
http://i193.photobucket.com/albums/z281/SHvar/Picture346.jpg
I to believe that regardless if the AR/M16 design being used for over 40 years in our countries military, it will probably be the last DI rifle used in its service. Being a combat vet that went to war with the M-16A2, I liked it, I trusted it, I mantained it, and it worked. In the conditions it worked, but religious maintance is needed on a daily basis. Its not hard to see why it sometimes fails in the nasty gritty dirty deserts with more frequent fire fights than if kept constantly clean. Keep in mind I had no complaint with the M16A2 (a full sized rifle with full sized gas system) neither did the Marines that used the M-16A4, today most soldiers are using the M4 which is more sensitive to the dirty environment, and more sensitive to lack of maintance.

gator-1
March 1, 2010, 03:25 AM
Wow The video on utube was very informative and the info and opinions here has been very helpful. Thanks I may wait awhile and see how the gas piston develops. Thanks again

NWCP
March 1, 2010, 03:58 AM
I own both a DI and a piston AR. Having been introduced to the piston concept with the CZ VZ58 I went for the Stag Arms Model 8. The VZ58 is a snap to clean and has worked flawlessly. I have no doubt the Stag will as well. Stag has addressed the issue of carrier tilt and designed their piston rifle accordingly. My RRA DI is fun to shoot and has been very dependable. I intend to use the Stag for hunting and my RRA as a personal defense weapon. The gas piston design isn't new technology and has been in service over 5 decades that I can think of. As for being nose heavy my Stag feels pretty well balanced and surprisingly light. No doubt the piston ARs may have teething problems. With the Stag Arms warranty I'm not particularly worried about it.

snakyjake
March 2, 2010, 12:41 AM
I don't believe the technology has been in the AR-15 for decades (we aren't talking AK47 or other rifles). But, is there some consensus on the top 3 AR-15 piston manufacturer designs? Any reviews/opinions of what designs are superior? What to look for? What are the criticisms?

LRS_Ranger
March 2, 2010, 08:36 PM
+1 for SHvar's post. I have shot everything from issue M16's and M4's, to very high end custom job piston systems. A properly tuned piston system shoots like butter, but then so does a very nice DI gun. I own an LWRC because I think that they are for all intents and purposes, equal, except that the piston runs wet and cool, and the DI runs hot and dry. A properly designed piston system is better than a DI system; if they were not, elite units that do a LOT of shooting and have expense accounts to pay for whatever they want wouldn't use them. There will always be resistance to change and rumors about how the "old" system is better. Take a while, go to the range, bring some 5.56, ask to shoot people's rifles, and see what you like best..

IdahoLT1
March 2, 2010, 09:16 PM
Based on several magazine reviews, the piston AR's tend/seem to be less accurate than the DI AR's

Boba Fett
March 2, 2010, 10:14 PM
Based on several magazine reviews, the piston AR's tend/seem to be less accurate than the DI AR's

That's interesting. I would have figured the opposite. How "less accurate" are we talking? Do you have any MOA comparisons?

Which magazines were you reading? Can I get to any of the articles online?


If true, it would really suck. I figured I'd get a piston AR once there was a history of use and wear and once there was a more common set of piston parts among manufacturers. If they are actually less accurate, I may just stick with the DI.

Hatterasguy
March 2, 2010, 10:21 PM
I have heard this to. Supposidly piston guns of any type are usualy slightly less accurite because you have the gas block mounted on the barrel.

DI guns don't have anything mounted on the barrel.

It does make sense in theory, having stuff mounted on the barrel doesn't help. But IMHO the difference is probably so small that I doubt most shooters are good enough to tell.

I mean could a DI Colt out shoot an LWRC because it has a piston? I don't beleive it could.

1858
March 2, 2010, 11:04 PM
I don't agree with the "gas piston ARs are less accurate than DI" statements. I haven't even started working up loads for my two POF ARs but I managed the group below (POF P308-20-MRR) at 100 yards with a scope mount that was moving every shot on the rail! Once I get over my recent surgery, I'm going to make a real effort with both POFs to work up loads that will put this BS to rest. If both rifles will consistently shoot under 1 MOA at 100 yards then I'll be more than happy.

http://128.171.62.162/hawthorn-engineering/thr/pof/p308_spr/range_targets/08-16-09/168gr_imr4895.jpg

:)

IdahoLT1
March 3, 2010, 12:03 AM
That's interesting. I would have figured the opposite. How "less accurate" are we talking? Do you have any MOA comparisons?

Which magazines were you reading? Can I get to any of the articles online?


If true, it would really suck. I figured I'd get a piston AR once there was a history of use and wear and once there was a more common set of piston parts among manufacturers. If they are actually less accurate, I may just stick with the DI.

Jan 2010 American Rifleman:
Para USA Tactical Target Rifle ($2400 MSRP)
16.5" barrel Delayed Impingement gas system
Average Extreme Spread accuracy: 1.97" @100yds
Best Average accuracy: 1.53"
Smallest 5 shot group: .98"

October 2008 American Rifleman
DPMS Panther 5.56 Sportical Carbine($699 MSRP)
16" barrel Direct Gas Impingement
Average Extreme Spread accuracy: 1.49"
Best Average Accuracy: 1.08"
Smallest 5 shot group: .98"

January 2009 American Rifleman
Charles Daily Defense D-M4LE($1239 MSRP)
16" barrel Gas Impingment
Average Extreme Spread: 1.49"
Best Average Accuracy: 1.21"
Smallest 5 Shot group: .98"

May 2009 American Rifleman
Les Baer Custom Police Special($1690 MSRP)
16" barrel Gas Impingement
Average Extreme Spread: .84"
Best Average Accuracy: .76"
Samllest 5-shot group: .61"

September 2009 Shooting Times
Les Baer Custom Police Special($1690 MSRP)
16" barrel gas imingement
Average Extreme Spread: .90"
Best Average Group: .71"
Smallest 5 shot group: .66"

-----------------------------------------------

January 2009 Shooting Times
Lewis Machine & Tool(LMT) CQB MRP PS16($1995 MSRP)
16" barrel gas-Piston operated action
Average Extreme Spread: 2.15"
Best Average Group: 1.87"
Smallest 5 shot group: 1.15"


October 2009 American Rifleman
Ruger SR-556($1995 MSRP)
16.26" Barrel Gas-Piston operated
Average Extreme Spread: 1.7"
Best Average Group: 1.43"
Best 5 shot group: 1.13"

October 2009 American Rifleman
Sig Sauer 556 Classic ($2249 MSRP)
17" barrel gas-piston operated action
Average Extreme Spread 1.82"
Best Average Group: 1.49"
Smallest 5-shot group: 1.26"

January 2010 American Rifleman
Sig Sauer 516($1300 MSRP)
16" barrel gas-piston operated
Average Extreme Spread: 1.47"
Best Average Group: 1.12"
Best 5 shot group: .89"

Tirod
March 3, 2010, 09:19 AM
All a DI or piston does is change the way an AR bolt unlocks. The DI gun directs gas into the bolt carrier group. It expands in that sealed chamber and causes the bolt carrier to move backward, which rotates the bolt by the ramp and pin disengaging the lugs.

A piston gun propels the BCG backward by directed thrust on a lug that replaces the gas key, exactly the way the charging handle does. The BCG moves backward and the lugs unlock.

Once the lugs unlock, the main thrust of the bolt comes from the cartridge itself, which still has the residual pressure of the gas that hasn't escaped from the muzzle.

If - if - piston guns have a problem with carrier tilt, it could be assumed to be coming from residual pressure from the piston rod acting on the lump. It appears some piston makers are tinkering with the BCG to improve it's reaction when it gets to the buffer tube. I haven't seen reports of this being a major problem with DI guns. That could be because they don't have thrust directed on the gas key - it all comes from the cartridge base.

This is a good example of why retrofitting the AR with a piston is still a problem. Having multiple proprietary designs doesn't help either.

The claim that they run cleaner and take less lube has to be balanced with cost: how much does a person shoot to justify the $400 expense, does it really give increased reliability over DI, and how much expense in lubricating a DI gun to keep it wet are you really saving?

The carbine pro's run them wet, keep them wet, shoot them wet, store them wet, and don't seem to have a problem with that practice. It's when they are run dry that problems come up.

Dry is the problem.

Why is the piston system The Answer? Because gunmakers can sell pistons, selling Mobil One, CLP, or whatever doesn't make them as much profit.

rangerruck
March 3, 2010, 10:23 AM
I am more in line with shvar, and 1858 here; I think the pistons are great, not front heavy, not less accurate, and operate at much less temps, and it is high heat that tends to destroy things- anything- quicker than anything else.
Piston drive ar's typically have parts that can be touched by hand, after firing multiple rounds; you could never do this with any part of a gas/di AR.
plus if you wanna do a conversion, a very good app. is the Osprey Defense, it has been tested by several folks here, including some police officers and other operators, and has thus far had no complaints, and seems to be 100% effective and reliable.
http://gaspiston.com/product/ops-416-for-carbine-length-guns/
http://www.youtube.com/watch?v=H8ho-5gSPWg&feature=related

watch this video, and where this guy is touching...

winknplink
March 3, 2010, 11:33 AM
the premium on a piston ar is what? roughly ~$400-$500

And a good BCG costs what? ~$200?...that's 2 bcg's you can burn up with DI and still be money ahead. SO, the economic standpoint is a wash, b/c by the time you shoot enough rounds to eat up 3 BCG's, your lower and barrel are gonna be pretty sloppy anyway, no matter which system you choose. My .02

to me, it boils down to not liking to clean a weapon = I will pay the premium.

clem
March 3, 2010, 11:34 AM
I have a lot of experiance with the M16 in Vietnam. It sucked.

I just put a Ruger SAR556 (piston rifle) on lay-a-way. I still don't like the 5.56mm for combat but for a zombie rifle it should be okay.

winknplink
March 3, 2010, 11:37 AM
I have a lot of experiance with the M16 in Vietnam. It sucked.

I'm going to assume this was before forward assist and chrome-lined barrels...early in Vietnam?

MachIVshooter
March 3, 2010, 11:57 AM
DI has worked well for half a century. It's lighter and cheaper. I'll stick with it. YMMV.

Once the lugs unlock, the main thrust of the bolt comes from the cartridge itself, which still has the residual pressure of the gas that hasn't escaped from the muzzle

That statement couldn't be more wrong. Inertia is what keeps the bolt (or slide, on a pistol) moving rearward after the breech unlocks. If you still have chamber pressure after the bolt unlocks, your firearm is broken and dangerous to use.

SHvar
March 3, 2010, 12:07 PM
Its not an accuracy issue with the piston, its an accuracy issue with the shooter not being able to hold the rifle as consistantly on target with the gas piston system acting on the barrel. The DI system is so broadly used for the simple reason that almost anyone can fire accurately with one, the piston system adds a percieved increase in recoil, it adds another moving part not in line with the bolt, barrel, and stock, so therefore theres more barrel rise.
I remember reading about the first impressions with the H&K416 that the special forces were using, they were initially having problems with accuracy, the rifle has a short barrel, a piston moving above the barrel out of line with the barrel, and took getting used to.
For the total difference of around $300 I got a gas piston rifle over another DI rifle, the fact that it runs 10,000 times cleaner is just a pleasant side effect, the fact that it runs so much cooler amazes me still.
If I lube a DI rifle down like I normally do, then add a bit before shooting, the bolt carrier is dry, cruddy, hot in a few rds.
Heck I dont mind cleaning them, its part of the fun of shooting them, but the fact remains that I can fire 200-400 rds in a day and spend 20 minutes taking my time cleaning my gas piston rifle, then work on another firearm I was using that day.
If I fire 100 rds through my DI rifle, or any other for that matter, and I clean it using the good old fashion way I used on my piston rifle (not using my powder blast or any other spray cleaner) Ill be busy for a good part of the evening.
Gas pistons were made for the AR rifle system for the simple reason that the DI system has serious shortcomings, one of those is the hours of cleaning and constant oiling required. Why did our military ask for a much more reliable system to be designed for them? Simple when it comes to the nasty gritty dirty desert, and faced with long drawn out firefights and attacks that can come at any time our soldiers werent always able to rely on the M4 to work every time.
Like I said before, if you religiously clean and oil an AR/M16/M4, between uses, while in the desert while not using every day, between every sandstorm, after every trip down a dusty road on a vehicle, you may not have a single problem. But the enemy doesnt wait for you to clean your weapon then reasseble it multiple times a day, they would much rather know when you clean it to attack you.

winknplink
March 3, 2010, 12:20 PM
^ I thought that was what the SCAR was for? A real, purpose-designed, piston-operated weapon?

Compared to the SCAR, a piston-driven AR is not much more than lipstick on a pig, right? Seems to me they are reinventing the wheel, when the wheel worked fine (insert plucked-from-air high percentage number here) of the time is areas not containing sandstorms.

eddism
March 3, 2010, 12:28 PM
H & K 416 is piston driven. It is one to be replacing the M4. Firing rate is around 800 rounds/minute. Piston is in the block itself and is tilt-type. It has burst capability as well as semi-auto. Full breakdown and demonstration of the piston-drive (in slowmo) can be seen on the Military Channel feed where I viewed it. They are high dollar at GunBroker and several can be found. Class3.com out of Florida has them for sale last I heard.

Unless you truly need full-auto capability. It dont make sense to have a piston-driven AR that toggles at the block like the H&K, in lieu of an inline gas blow-back at the bolt AR-15. You cant fire enough rounds in semi-auto to make a meaningful difference. But, if the H&K 416 fits your eye and wallet. Piston-driven AR's are found to be more reliable when pitted against their counter-part top line in-line gas-blowback AR-15's.

Boba Fett
March 3, 2010, 02:30 PM
IdahoLT1

Thanks for the info IdahoLT1!

Going to have to see if I can find those issues now...

Boba Fett
March 3, 2010, 02:44 PM
Piston drive ar's typically have parts that can be touched by hand, after firing multiple rounds; you could never do this with any part of a gas/di AR.

Piston ARs also have parts that can't be touched. The heat is just in a different location.

http://www.youtube.com/watch?v=6auXTiqNtEo
Watch time at: 16:43
You should watch it all, but that section talks about the heat.

Bartholomew Roberts
March 3, 2010, 03:40 PM
If I lube a DI rifle down like I normally do, then add a bit before shooting, the bolt carrier is dry, cruddy, hot in a few rds.
Heck I dont mind cleaning them, its part of the fun of shooting them, but the fact remains that I can fire 200-400 rds in a day and spend 20 minutes taking my time cleaning my gas piston rifle, then work on another firearm I was using that day.
If I fire 100 rds through my DI rifle, or any other for that matter, and I clean it using the good old fashion way I used on my piston rifle (not using my powder blast or any other spray cleaner) Ill be busy for a good part of the evening.

This article describes all you need to keep a direct impingement AR15 functionally clean (http://www.ar15.com/content/swat/keepitrunning.pdf) and it doesn't take more than 15 minutes to do it - even after 400 rounds.

The instructor who wrote the question now has a direct impingement rifle (BCM midlength) that will exceed 30,000 rounds with NO cleaning of any kind. All they did was add more lube periodically. He has several more that are in excess of 10,000 rounds.

The heat is just in a different location.

Yeah, typically it seems like gas piston manufacturers like to vent heat either right in front of my optics or right where my offhand is.

winknplink
March 3, 2010, 03:57 PM
Boba, thanks for that link...very informative.

1858
March 3, 2010, 06:38 PM
IdahoLT1, if you're trying to make an "apples to apples" comparison between DGI and GP ARs in terms of accuracy, wouldn't it make sense to shoot some groups with a DGI AR, then retrofit a GP kit and shoot some more groups. At the very least, compare an LMT, Bushmaster etc. standard DGI AR with one of their GP variants. Then you might have some meaningful data. As it stands, that list is meaningless. Good grief, most rifles weren't shot in the same month let alone on the same day, some not even in the same year!! How about ammunition used? What about barrel differences such as twist rate or type of manufacturing.

:)

clem
March 3, 2010, 10:34 PM
Go here and read this:

"The Last “Big Lie” of Vietnam Kills U. S. Soldiers in Iraq"


http://www.thebutter-cutter.com/Last_Big_Lie_Of_VNhtml.html

rangerruck
March 4, 2010, 01:01 AM
boba fett; you are right, like the muzzle/flash supressor, and the piston itself.
but the piston cools down very fast, and neither are what you would consider, very likely to break down from heat/filth, anytime soon!!!!

C-grunt
March 4, 2010, 01:31 AM
Gas pistonswere made for the AR rifle system for the simple reason that the DI system has serious shortcomings, one of those is the hours of cleaning and constant oiling required. Why did our military ask for a much more reliable system to be designed for them? Simple when it comes to the nasty gritty dirty desert, and faced with long drawn out firefights and attacks that can come at any time our soldiers werent always able to rely on the M4 to work every time.
Like I said before, if you religiously clean and oil an AR/M16/M4, between uses, while in the desert while not using every day, between every sandstorm, after every trip down a dusty road on a vehicle, you may not have a single problem. But the enemy doesnt wait for you to clean your weapon then reasseble it multiple times a day, they would much rather know when you clean it to attack you.

The M16/M4 does not need to be cleaned that often. We would do a quick wipe down after a mission, 5 minutes, and a good cleaning every week or so. My unit never had problems with our weapons, save for a few of the M249s.

With a mag in and the dust cover closed, very little dust will get in the rifle. During the invasion we actually fought during the huge red sand storm and two days after. Our rifles still worked.

Also the rifle doesnt have to be inspection clean to run. Wipe the bolt and carrier down and clean out the chamber and the lugs. Wipe down the inside of the upper reciever where the BCG rides. You dont need to clean the carbon in the rear of the reciever above the charging handle for the weapon to run well.

SlamFire1
March 4, 2010, 09:45 AM
Soldiers are always sensitive to criticism of their equipment. They are issued a weapon, get used to its faults, and they donít get to use the alternatives.

The direct impingement gas system of the M16 is an evolutionary dead end. It will be continued to be used in the Civilian sector (AR-10 copies for example), but no service rifle in the world is using the system. Neither is the system being used in squad automatic weapons.

It was not best of its class, it will never be best of its class, it is sticking around because it is too costly to replace, and too politically difficult to overcome the Colt monopoly on Capital Hill.

Tirod
March 4, 2010, 10:20 AM
That statement couldn't be more wrong. Inertia is what keeps the bolt (or slide, on a pistol) moving rearward after the breech unlocks. If you still have chamber pressure after the bolt unlocks, your firearm is broken and dangerous to use.

Inertia is driven by the cartridge face pushing the locked open BCG. On DI or roller locked guns, there is NO operating rod to do the job. ONLY the cartridge face pushing the bolt backwards can do it.

Dispensing with blot lugs entirely, blowback from the pressure in the cartridge case is the only thing that makes .22's, .32's, and .380's semi autos work at all.

The 9mm AR pistol and carbine conversions dispense with the gas action entirely. Straight blowback. There is no DI system, a special bolt, and the dedicated uppers don't have the gas tube hole in them.

AR's not ejecting or cycling correctly are sometimes diagnosed as "short cycling." The cause of that is ammo with low powder quantities that produce sub optimal gas pressure. There's enough to unlock the bolt, but not enough left in the barrel to push the cartridge case against the bolt to fully cycle the action. According to pressure graphs, that pressure is an initial peak that tapers at the bullet travels the barrel and exits. The bolt doesn't unlock until then - and the residual barrel pressure in the cartridge case then moves the bolt backward to cycle the action. That's because gas will exert pressure on 360* of the interior of the object containing it.

Pistons don't change any of that, properly designed, they just move the bolt differently in the unlocking phase. Whether it's worth $400 to excuse cleaning a rifle properly is bogus. It's a long standing myth that they need extensive and intimate cleaning on a demanding schedule. That old chestnut has is based on a 45 year old problem long ago solved when the ammo was changed to the correct powder, cleaning kits were issued one per rifle, and Ordnance regained their directive position - telling one and all to clean the weapon periodically - AND LUBE IT.

I can buy more lube for $400 than I will use in my lifetime of shooting AR's. Piston conversions are a marketing exercise exploiting the technical ignorance of a gullible public.

MachIVshooter
March 4, 2010, 10:44 AM
Inertia is driven by the cartridge face pushing the locked open BCG. On DI or roller locked guns, there is NO operating rod to do the job. ONLY the cartridge face pushing the bolt backwards can do it.

Dispensing with blot lugs entirely, blowback from the pressure in the cartridge case is the only thing that makes .22's, .32's, and .380's semi autos work at all.

Still wrong. There is still some pressure as the case begins to extract. But by the time the case mouth clears the breech, the bullet has left the barrel. No more pressure, just momentum of the slide.

In roller delayed, short or long recoil operated locked breech, or gas operated weapons, the bullet is out of the barrel by the time the action unlocks. The bolt has already begun moving rearward before the lugs unlock, and that momentum continues to move the BCG after the pressure has dropped. What happens when the bolt opens before the bullet has left the barrel can be seen in any instance of out-of-battery firing, in which the case usually ruptures and the action cycles very violently. You also end up with a face full of debris that was spewed out of the action because it opened too soon, while there was still pressure in the bore and chamber.

If it were only the rearward force of the cartridge case under pressure that moved the bolt backward through it's entire range of travel, we wouldn't need extractors. There are a handful of small caliber blowback guns that will cycle without extractors (Beretta 950 BS, for example), because they are timed to operate that way. But for most blowback, and ALL locked breech weapons, the pressure is gone by the time the action opens, and the case will not push itself out under gas pressure. It must be extracted, and this is done by the mechanical extractor attached to the BCG or slide that continues to move with inertia alone.

SlamFire1
March 4, 2010, 10:46 AM
That statement couldn't be more wrong. Inertia is what keeps the bolt (or slide, on a pistol) moving rearward after the breech unlocks. If you still have chamber pressure after the bolt unlocks, your firearm is broken and dangerous to use.

All semiauto mechanisms are designed to unlock when there is residue pressure in the chamber. The unlock must occur at a pressure below the rupture strength of the cartridge.

This is why case life is so low in Garands and M1a's, the case is being stretched during extraction.

The residual breech pressure is measured and the action is timed to open to make the maximum use of the energy available.

This also explains why there are warnings about port pressures and slow burning powders.

In this Army Design manual they measured the residual pressure curve of the 308 and 30 Carbine because they needed this information in the design of the weapons.


http://img.photobucket.com/albums/v479/SlamFire/Reloading/Pressuretimecurve762NatoAMCP706-260.jpg

http://img.photobucket.com/albums/v479/SlamFire/Reloading/30CarbinePressuretimecurveAMCP706-2.jpg

MachIVshooter
March 4, 2010, 10:54 AM
Slamfire-

We're not debating that there is some residual pressure as the case begins to extract. The subject here is that it is not that pressure that causes the action to cycle after the bolt unlocks, but the momentum of the BCG that is already traveling rearward from actions induced when the pressures were still high.

Anyone who doubts that it is strictly the momentum of the BGC that provided the thrust need only remove their extractor and witness that there is insufficient pressure to even push the case out of the chamber, let alone move the bolt.

Dravur
March 4, 2010, 11:00 AM
I have heard many people say that the Piston guns run cleaner than the DI guns and I have a question....

The same amount of gas/gunk/etc comes out the gas hole in either case. That stuff has to go somewhere, so either it goes in the piston, or the upper.

Is that true?

winknplink
March 4, 2010, 11:03 AM
Drav, watch the video Bobba posted yesterday, about half a page up from here. Good stuff.

MachIVshooter
March 4, 2010, 11:13 AM
Here, for the naysayers:

http://www.youtube.com/watch?v=l5PHkv3f-9U

http://www.youtube.com/watch?v=GEJUoNfR6Wk&NR=1&feature=fvwp

http://www.youtube.com/watch?v=SgldaFmgPZo&feature=SeriesPlayList&p=E06854DC45008B62

http://www.youtube.com/watch?v=_cXGNarToO8&feature=SeriesPlayList&p=E06854DC45008B62

http://www.youtube.com/watch?v=zVwSFEZMB_Q

http://www.youtube.com/watch?v=G0VjdI_S_HM&feature=related

In every one of these, you can see the plume at the muzzle behind the bullet before the slide or bolt handle moves far enough to unlock the action

Dr. Tad Hussein Winslow
March 4, 2010, 11:18 AM
for a short answer, DI is lighter and just as good - that makes it preferable for most purposes.

for long answer, see above.

Now if I may be fighting in dirt, dust, & mud for long periods of time without cleaning, then I'm gonna go with a longstroke Kalashnikov action (i.e. a Robinson XCR), not a piston AR using a short-stroke piston system.

Since I don't 'fight' at all (fingers crossed), let alone in dirt, dust, & mud for long periods of time without cleaning, the DI guns (AR15 types, AR10 types) are *perfect* for me (and most people).

SHvar
March 4, 2010, 12:28 PM
Depends, at one time I did fight in the desert, and I never had a problem with a DI full sized rifle, didnt have a carbine to compare it to then. I cleaned daily, and yes it depends where you are at the time you can see sandstorms almost daily (depends on the weather and time of year), in fact depends how nasty it got I cleaned 2 times a day and kept as much of the rifle covered as possible (guess what sands still gets all through it).
Heck I had a malfunction in training once with the M16, it was after almost a month of training in the mountains, while the OPFOR attacked, I cleared the problem, and continued, but it was due to long days, and not enough maintance (I was getting my cleaning kit out to clean right before it happened). Keep in mind it was not in the sand, it was actually nice calm weather, and very little rain in that time.
By the way when you fire a piston AR the piston assembly gets hot, but cools down fast, and its not an area of the rifle that is affected by the heat, grit, carbon, burnt oil, and wont cause it to malfunction.
Also when I fire my gas piston AR the hot gases dont effect my optics, or sights, nor does it heat my hand, or the handguard up.
Yes a GP AR is more difficult to fire as accurate, but thats not a problem in the rifles design, or function, nor will that ever cause it to malfunction under strenuous conditions.
The primary reason DI rifles are used in so many cases in the military is the fact that they are so easy to fire accurately, this allows you to make use of more soldiers with less stringent training, allows you to qualify higher numbers in a shorter amount of time.
Theres nothing wrong with DI rifle if used corectly, if maintained like your life depends on it. The GP is just an option that allows for a more broad range of uses under more extreme of conditions.
They are fun to shoot, Im glad I bought one.

C-grunt
March 4, 2010, 08:31 PM
For the record, Im not against the piston rifles. In fact I almost bought a POF today, but ended up getting a Noveske.

The pistons ARs are still in their infancy and havent shown what their problems really are yet. Once they get some experience and history, as well as a standardized system, I will be much more into them.

I know the shortcommings of the DI system and know how to avoid and fix them.

Tirod
March 5, 2010, 09:04 PM
Sure, bolts have extractors, but on blowback actions, nothing touches the bolt other than the case. The case pushes the bolt backward, and the case is pressurized by gas in the barrel.

On a submachine gun using advanced primer ignition, the firing pin is dimensionally optimized to ignite the primer before the bolt is fully seated. Momentum - or the moving inertia - of the bolt is used to keep the bolt closed until the bullet leaves the barrel. Once gas pressure has built up enough to overcome bolt momentum, it then pushes the cartridge face against the bolt to cycle the action.

Extractors are part and parcel of unloading unfired ammo, and controlling the way the case is propelled out the ejection port. Cases that stick in the chamber due to excessive expansion will not extract and sometimes suffer case head separation - if the extractor is sharp and maintains a grip.

Here's where things get confusing. Systems that impart energy to the bolt by DI or piston react differently than systems that use the case to move the bolt. DI and piston systems start a part of the bolt moving to unlock it. Blowback systems use the case to impart movement to the bolt.

In some sub gun systems, the chamber is even designed to overexpand the case to delay bolt movement by absorbing energy to literally resize the case - and delay or prevent premature extraction of the cartridge that could cause case wall failure. The stainless 9mm Pocket Pal also used the technique. It's also a good example of the force vectors involved. Rearward propulsion of the case out the chamber was so high delay was necessary to properly time the action cycle.

It's not the extractor doing that, it's a gas pressurized case cycling the action.

In a short action piston conversion for the AR - short meaning the travel of the piston is less than cartridge length - the piston rod strikes the lump with enough force to propel the bolt carrier group the full length of the action, compressing the spring. In a submachine gun, the case does that. In a DI gun, it's entirely possible the rearward movement of the bolt carrier group could be doing that. One thing that leads me to think about the case still pushing on the bolt face is that once the bolt is unlocked, the pin moves into alignment with the gas key slot - which prevents the bolt from rotating back into the locked position while cycling.

Some would have it that there is a lot of pressure on the bolt face during cycling trying to collapse it - and even sell a roller bearing to relieve the pin pressure in the upper. I conclude Stoner knew the case was pushing pretty hard on the bolt face and not just getting pulled along for the ride.

Haven't even touched on recoil operated mechanisms - which is the whole barrel moving backward against the gas pressure pushing the bullet forward.

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