piston vs direct impingemet m16

Chivers is a journalist who is actually qualified to write about firearms. I like his stuff.

I'm not a big fan of the piston guns as there is no set standard yet and everyone makes their own proprietary system. That being said the SWAT team on my dept uses POF rifles and they have held up very well with the high amount of rounds they put through them. They are a bit heavy though.

Well if you compare two different rifles with two different operating systems, then any difference in performance must be a result of the operating system choice, right?

For example, just using the 5oz heavier M4A1 SOCOM barrel will let the M4 go from the 536 rounds seen in that test to 900+ rounds with no barrel burst (though it does go bolt action around 911 IRRC). So almost twice the round count; but with no change in the operating system.

Not sure what the barrel profile of the P-416 is; but it does use a little bit bigger barrel nut than the M4 - one that the manufacturer claims dissipates heat 5 times faster and probably accounts for some of the weight difference C-Grunt noticed. If I had to guess, I am betting that played a larger role than the operating system.



And naturally, all of this information is vital for when you have to dump 535 rounds ($214 worth of brass-cased FMJ ammo) downrange in less than 2 minutes. That happens all the time.

After action report indicates they should maybe find a way to protect heavy guns from small arms fire rather than use small arms as heavy arms. In the first article what is being compared? How does a barrel failure or gas tube failure reflect on impingement system? According to the article, peak temps were lower in the M4. It proves the upper they used was more reliable than a standard M4 for full auto from a tripod.
Isn't that what machine guns are for?
I hear new trials are underway for improvements to the carbine. I'm all for improvements. Gimmicks not so much.

Um, yeah, what he said
I don't understand why you would sacrifice the SIMPLICITY of the DI system (even if it does require more cleaning - not I didn't say maintenance)

for a HEAVIER, more complicated system with more parts to break or just go wrong. What happens if you are over gassed from using plinking rounds or undergassed when you really need it.

I'm not a big fan of the piston guns as there is no set standard yet and everyone makes their own proprietary system

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Agreed. This is the only real problem I see with the pistons. It makes sense to me that pistons are the next evolution of the AR platform and once a standard is set it will take off. I can't think of another system that has evolved like the the AR and most of the changes have worked out.

I never though cleaning my AR was all that difficult. I no longer subscribe to the military standard of being able to eat off the chamber, but I get it clean. And it is not hard. At all. Even when I only clean it every few thousand rounds.

Piston guns are fine if that is what your want. It's your money, go nuts. To me it is a solution looking for a problem.

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Same here. I spend at most about 10 minutes cleaning my AR (pull a boresnake through the barrel a couple times, wipe down the BCG and relube). Never had the slightest issue.

Most of the crap that ends up in the chamber comes out of the spent case itself anyway. So if your goal is to eliminate chamber fouling, switching to a piston system on an AR is like putting a bandaid on a broken leg. When shooting dirty surplus ammo (Wolf) in my AR, M-1, SKS or an AK I used to own, all four get/got crudded up about the same. The only difference I can discern is that the piston driven guns spread the crud over more parts.

Piston guns introduce problems not found with DI. Carrier tilt, RE wear issues need to be addressed. Proprietary parts is a major draw back. I'll keep my pistons where they belong, on Garand's, Carbine's and M14's.

(direct impingement) Less parts, Less to go wrong................

Never had a problem keeping my "old school" ARs running but I can understand why companies want to have piles of piston uppers ready for sale. Just like the Pet Rock, how can you call a guy a fool that can sell rocks for $5 each.

I was once involved in a training exercise where I put 14 magazines through my M4A1 all on full auto in the course of something like 8 minutes. I did not experience any malfunctions and I developed a new respect for DI and a new skepticism about all the piston designs being that much better.

I like to think of acceptable reliability in terms of the rifle being able to fire (without a malfunction) the amount of ammo that I'm willing to carry on my person. Anything beyond that is great, but I won't pay more for something that I will not ever use just to say that I could if I needed to.

I see I'm in the minority here. I've had Direct Impingement (DI) ARs and always hated how dirty they ran. The the gas tube makes the hand guard hot after a couple of magazines and the spent gas going into the BCG made the receiver hot too. I've noticed that several people here say cleaning a DI AR only takes a couple of minutes but I'm not sure what kind of minute they're talking about. I don't believe you have to make a gun "white glove" clean but even so it takes time to disassemble the BCG on an AR to clean it! DI BCGs get covered inside and out with spent gas residue.

When I fired my first piston AR, I was hooked! Yes there are more parts, (mine have 4 more than a DI gun), and the piston weighs more than a gas tube but IMO those are small issues! I'll take the extra few ounces of weight as a trade off for a cleaner, cooler running gun. Other people cry out "carrier tilt"... If I'm not mistaken, a piston gun and a DI gun exert pressure at the same point on the BC group, just differently. I haven't noticed any unusual wear on my piston guns, so I'll have to wait until I see something I don't see on a DI gun.

My piston guns run MUCH cooler too! I can fire 2 or 3 magazines through my ARs and the hand guard although warm up by the gas block, is cool to the touch everywhere else. The BC group is still pretty much "room temp" to the touch after firing as well. Don't try that with a DI system, you'll leave your finger tips burnt onto it! Also after I'm done shooting, the only real cleaning needed is the barrel and gas block. The BC group is still clean but you may want to use a Q-tip on the bolt face...no biggie. One other thing I like is, although the .223 doesn't have much in the way of recoil, my piston guns seem to have less felt recoil. All in all, I'll take my piston guns over the DI guns. Just my opinion...

http://www.youtube.com/watch?v=unYAcHIUhXE&feature=youtube_gdata_player

DI seems to operate fine with A LITTLE water.


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DI makes for a fine target weapon but that red hot gas tube sure makes me wonder why we ever adopted DI for a service weapon.

The answer has to be politics.

The NYT writer/author Chivers, who also wrote "The Gun" (about the AK and M-16's development) was an infantry officer in the US Marine Corps.

You might still be able to read short excerpts of "The Gun" on Amazon.

You can buy 'The Gun' for $16 new or as little as $4.32 used (http://www.amazon.com/The-Gun-C-J-Chivers/dp/B004Q7E0YA/ref=sr_1_1?ie=UTF8&qid=1336939853&sr=8-1). IMO it's a pretty good book. It's not just about the AK either, it traces the development of the Maxim and other rapid fire infantry arms that preceded the AK.

Personally I don't see anything wrong with DI. It's anecdotal, but I once ran 3,000 rounds through a M4 in two days at work and only had 1 malfunction, and that one was clearly the mag's fault. My only complaint, if you can call it that, is cleaning out the inside of the bolt carrier afterwards.

I have both and run both pretty often. My favorite is my A2 clone, but I trust my life everyday to a piston conversion gun I built.
BC tilt is a non issue unless you go cheap and only switch out the gas key instead of the bolt carrier.
Persoanlly I've noticed no reliability issues, or displaced fouling issues in my piston gun. The only part I've changed out since the conversion is the extractor and extractor spring. My uppers no where near as dirty after a range session either.
But to each his own I guess.

SlamFire1 said:

DI makes for a fine target weapon but that red hot gas tube sure makes me wonder why we ever adopted DI for a service weapon.

The answer has to be politics.

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Huh? A red hot gas tube after hundreds of full auto rounds concerns you? DI was adopted because it is a better system for this gun. It works just great in a combat weapon.

I suggest a few of you look up the temperature differences between a DI piston and normal Piston design. It is very minor.

In my limited experience in highpower matches, 75% of the alibi strings are M1A's. 90% of the guns on the line are AR-15's. To me, the math seems to be in favor of the DI system. I find it very tolerant of various ammo combinations compared to my piston guns.

Not all piston AR's are the same. Check out the long-stroke system from PWS. It is different than the POF/LWRC/Adam's and other short-stroke systems out there.

GTimothy said:

If I'm not mistaken, a piston gun and a DI gun exert pressure at the same point on the BC group, just differently.

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You are mistaken. A piston exerts force above the line of the bore against the gas key. In DI the gas flows through the gas key to fill the space between the gas rings and the bolt carrier group, as the bolt carrier group is pushed backwards directly in line with the bore, the two holes on the side of the bolt carrier group pass aft of the gas rings and the excess gas is vented out the ejection port through those holes.

The reason this is an issue in ARs is because the bolt carrier was never designed to ride in rails to counter the off-axis force; because there was no off-axis force. So most gas-piston AR designs spend a lot of time figuring out how to counteract this problem; but still use AR receivers not designed for that.

The BC group is still pretty much "room temp" to the touch after firing as well. Don't try that with a DI system, you'll leave your finger tips burnt onto it!

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There is around a 40deg difference in the bolt temperatur of a Colt M4 and Ruger SR556 after rapid firing 5 mags.. However, there is still another reason not to try shotgunning the bolt and dumping it in your bare hand immediately after multiple mag dumps - that whole "serves no practical purpose" thing.

dprice3844444 said:

it proved that in an severely extreme scenario,the gas piston and heavy barrel were the way to go.

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Did it? It looks to me like it suggests that the P-416, which has a heavy fluted barrel (according to their website) and a 3.5oz barrel nut/heat sink handles heat better than an M4 on full auto. Though it is hard to compare directly since one is a magazine writer blasting away semi-scientifcally and the other is a professional testing lab conducting a test under controlled conditions. You seem to be assuming that the difference is due to the operating system rather than the extra barrel mass and heat sink/barrel nut. Why is that?

I've fired several full auto mag dumps through a piston HK 416 (10.4") and, sure enough, the bolt carrrier remained about room temp. However, the railed handguards were extremely hot. I don't know about you, but I usually hold the handguards when I shoot, not the bolt carrier. It was also quite a bit heavier than the 14.5" M4 with similar optics.

I've also fired many, many full auto mag dumps with DI M4s. Not always one, but often 3 or 4 mags through M4s with 15,000 rounds through them already. The handguards got a little warm, but not bad and I never thought about popping the bolt carrier out for a little feel.

You know, I didn't want to like the DI M4, but after putting untold numbers of rounds through them in all sorts of configurations, they work and they work well. They've won me over.