Gas Piston vs Direct Impingement Actions

[Crash]

Following is a quote from the Armalite web-site concerning cleanliness of gas piston vs direct impingement actions:

"There is a debate about which system remains cleanest. The Stoner system tends to leave propellant residue in the receivers, while the Piston systems keep the residue outside the action in the cylinder. Piston driven systems, however, tend to allow more external dirt into the action because of the openings required for various connecting members (operating rod, bolt lugs, etc). Comparison tests of the Stoner and the M-14 before Desert Storm confirmed the superiority of the Stoner system in sand and dust tests"

Is the last sentence true/correct? I've always heard that gas piston systems are less likely to jam due to fouling vs direct impingement systems.

Crash

[Matthew]

I'd say it is a fact. If you look at two 5.56 rifles in service today, the AR15 and the British SA80, which is gas piston operated, the AR15 blows it away.

Here's a link to see some pics of the SA80. You can see the openings that Armalite was talking about in the piston type rifles.

ETA: Duh the link would be nice. ::)

http://world.guns.ru/assault/as22-e.htm

[jim]

Through experience, I've found that the gas inpingement system to be inferior to the gas piston/op rod systems. The M14, and AK are far more reliable rifles than an AR. The AR system in a 7.62 NATO round are more reliable than the 5.56 models. It all has to do with chamber demensions and powder residue.

The 5.56 and original AR was designed to use IMR4895, and the US Army decided to use ball powders which contained calcium carbonate that caused the plague of malfunctions. Once the calcium was removed, then most of the problems went away.

Without expanding ammunition the 5.56 is good only to cause wounds and is no man-stopper. A larger caliber is needed.

jim

[Crash]

Jim,

I've never fired an M1A and haven't fired the M16 or its variants very much, but I've sure heard a lot of reports from Vietnam and Afghanistan and Iraq of jamming problems when it gets dirty. On the other hand, I've fired many hundreds of rounds through AK47s, AKMs, and AK74s and never had one single jam and reports from the battlefield attest to the AK's reliability.

Crash

[jim]

From what I've seen, the AK is about the best. To be the ultimate, I'd think it needs better sights, trigger, and a min of 2" groups at 100 meters.

jim

[Crash]

From what I've seen, the AK is about the best. To be the ultimate, I'd think it needs better sights, trigger, and a min of 2" groups at 100 meters.

jim

Jim,

Agree with you there, but with the loose clearances that contribute to an AK's reliability I don't think you'll ever get that kind of accuracy. It's been a while since I've fired any version of the AK, but as I remember it we were lucky to get 6" groups at 100 meters.

Crash

[dannanchieftain]

I have had experience with both types of weapons in the military and as much as I like the M16 Id have to say IMO the Gas piston system is more reliable.

Something that may not have been considered is in a gas piston system there is less heat generated on the bolt and in the action than the direct impingement system. This is why I beleive machineguns like the M60/M240 and the M249 use the Gas piston design. Although I think one flaw with the m60 was the floating piston, if it got obstructed there was nothing in the weapon to move the piston other than gas pressure and thus it would fail, for those that have been on the m60 remember tipping the barrel just before moving out to listen for free movement of the piston?. That problem was corrected on the M240 where the Gas piston is attached to the op rod and springs in the action could retract it if there was a minor obstruction. also the M240 has a selectable gas regulator with a larger orifice that can be used in dusty conditions.

There are other reports that say the Gas piston system is more reliable. The new H&K 416 is supposed to be an all weather all conditions redesign of the M4 and it has the Gas piston type system. It is supposed to be immune to dirt,dust and water. H&K claims thier system is better. If you have seen the show "futureweapons" on discovery there is an episode that features the 416 where he buries it in sand and fires it *without malfunction.You can check out the H&K 416 at:

http://www.hkpro.com/hk416.htm


I think what they were trying to do with the direct system was use some of the propelling gas to blow out any dirt in the action once the bolt cycled. I dont really think it does much of that.

One of the common problems I have seen with the M16 is that soldiers tend to over oil the bolt. When you add dirt,heat, and carbon from spent propellant it can lead to a malfunction

[Crash]

I have had experience with both types of weapons in the military and as much as I like the M16 Id have to say IMO the Gas piston system is more reliable.

Something that may not have been considered is in a gas piston system there is less heat generated on the bolt and in the action than the direct impingement system. This is why I beleive machineguns like the M60/M240 and the M249 use the Gas piston design. Although I think one flaw with the m60 was the floating piston, if it got obstructed there was nothing in the weapon to move the piston other than gas pressure and thus it would fail, for those that have been on the m60 remember tipping the barrel just before moving out to listen for free movement of the piston?. That problem was corrected on the M240 where the Gas piston is attached to the op rod and springs in the action could retract it if there was a minor obstruction. also the M240 has a selectable gas regulator with a larger orifice that can be used in dusty conditions.

There are other reports that say the Gas piston system is more reliable. The new H&K 416 is supposed to be an all weather all conditions redesign of the M4 and it has the Gas piston type system. It is supposed to be immune to dirt,dust and water. H&K claims thier system is better. If you have seen the show "futureweapons" on discovery there is an episode that features the 416 where he buries it in sand and fires it *without malfunction.You can check out the H&K 416 at:

http://www.hkpro.com/hk416.htm


I think what they were trying to do with the direct system was use some of the propelling gas to blow out any dirt in the action once the bolt cycled. I dont really think it does much of that.

One of the common problems I have seen with the M16 is that soldiers tend to over oil the bolt. When you add dirt,heat, and carbon from spent propellant it can lead to a malfunction

dannanchieftain,

The HK416 sure looks good. I have the utmost respect for all HK products and I know that the MP5 has a stellar reputation throughout the world.

Would love to have a semi-auto version of the HK416 with a 20" bbl. Or even better, a .308 version....


Crash

[Matthew]

Not to stir the pot, but I re-read the OP and the comparison was between the M14 and the M16 in a desert environment. Just based on those two weapons, I'd say Armalite's testing is true.

[Oblio13]

AR's and M16's are very reliable, but they like to be "wet". Keep them well oiled, and they'll keep running for hundreds and hundreds of rounds between cleanings.

The only time pistons really have an advantage is when suppressors are being used.

[Clem]

The M-14 and M-16 are very different weapons: the M-14 is an open design, which is designed to allow dirt out. The M-16 is a closed design, which tries to keep dirt out, but if it gets in, you are in trouble.

Someone already mentioned the power change by the Army. Not only did it increase the dirt accumulated in the action, but it also increased the port pressure, which resulted in higher cyclic rates, increasing damage and reliability issues.

The Army also ordered Colt to significantly tighten up internal clearances, which also had the effect of making the gun much more sensitive to intrusion of dirt.

I presume these issues have been delt with over that last 30 years. What I also heard in the summers during the heavy combat in Iraq was the overheating of the M-16/M-4s in the summer heat. What did they expect? Dumping very hot soot into the chamber, during those nice 125 degree days.

[Pitdog]

As a professional in the AR business, building, serviciing, repairing, testing, inspecting etc AR type rifles everyday, reliability is truly in the operator and the care taken of the individual rifle.
When comparing AK and AR piston systems, they are apples and pears, SIMILAR, but not exactly alike.
AR vs AK, AK has the edge due to style, design and tolerance. AR piston to AR direct......... well that is a slightly different story. IF you were in the harshest conditions on earth, the piston might go longer without needing to be cleaned, than direct, but quite honestly, they both need cleaning and maintenance to run properly. Current piston systems for the AR are still so closely toleranced, due to gas port diameters still made for the direct system, vs gas to regulate the extra weight of an op rod, (and a wimpy op rod at that) that I might add is easy to bend and manipulate- yes experience speaking! Effing up is party of the job sometimes LOL.
The AK has this ghetto booty sized Piston head that is solidly attached to the carrier assembly which has a sloppy as joe camming surface to lock a bolt closed that will fire despite headspace as long as the firing pin can reach the primer.
AR............ I did one test trying to get a bolt to fail, and fired litterally over 1500 rounds without failure out of a direct system, and the ammo was cheap and dirty, and I was REALLY trying to get it to fail. Vltor makes a fantastically high quality Piston upper, and I have had soem trouble getting them to run, generally once they are up and running, they take off ok, but I haven't noticed that they can do anything yet that the direct job will.
I think the real question is, how much money do you have and what are you using it for?

[jim]

Welcome back Matt, great to hear from ya!

Pit

A bit off topic, but what do you think of the Bushmasters? What bbl twist would you consider best for SS109 or a reasonable facsimily?

jim

[Pitdog]

1 in 9 will shoot anything well. 1 in 7 for shooting everything heavy! 1 in 7 will not shoot the 55 grain stuff as well. I'd say 9 will do you for occasional shooting of 62/69 gr while everyday shooting of 55's will be fine.