9 million piston guns can't be wrong.

[Tirod]

What is it, about 9 million M16/M4/AR15's built since the early '60s?

They are all piston guns, each and every one except the pistol caliber blowback versions. Direct Impingement may conjure up visions of some space gun action, it's actually a simple adaptation of the traditional gas action using a piston and cylinder.

Right? OK, pickup the carbine/rifle, shotgun it, pull out the BCG, remove cotter pin, firing pin, and cam pin, separate bolt from carrier.

Look at the bolt tail. Look at the gas rings. That's the piston head end. Look in the carrier. That's the gas cylinder. Gas comes in via the gas key, pressurizes the cylinder. The gas rings keep it from leaking out so it can do work. What it does is move the cylinder, not the piston - no law of mechanics broken there, either can move. As the carrier moves to the rear, the cam pin rotates the bolt unlocked, the upper channel keeps the bolt unlocked, and the BCG cycles the action.

It's a piston gun that has gas pressure directly impinging the bolt carrier to make the action cycle.

No specific agenda here, most just don't see it. If a piston gun is wanted, go for it. The expressed intent of many piston gun owners is to not have to clean it as much, fine. Don't clean the DI either, all the better grade guns keep on shooting anyway. Saying the DI is dirtier than Piston, no. Go look at either piston face after five magazines, they are both dirty. Saying the piston gun is cooler, no, get an IR thermometer gun and read the temps - piston guns at the cylinder on the barrel are much hotter than DI guns are in the carrier. Can you hold the Piston gun cylinder in your hand after a full mag dump? The DI carrier can be.

Where you choose to put the piston is your business, let's just keep an even playing field about it. Compare apples to apples, piston to piston, cylinder to cylinder, not op rod operated bolt carrier to DI bolt carrier. It's not just a DI carrier, it's the cylinder and piston, too.

Ok, piston back in cylinder, cam pin in, firing pin in, cotter pin in, unlock the bolt and insert into upper, close and push the pins in. Don't forget to be safe with your piston gun.

 

[Z-Michigan]

But, but, but - the piston location is BACKWARDS! How can that be?

Oh, btw, some piston guns, notably the M14/M1A, will lock up tight if you don't clean carbon out of the piston and cylinder. I have not heard of an AR locking up from lack of cleaning.

 

[Dionysusigma]

Lack of lubrication, though, yep.

If there is one thing that piston-uppered guns tend to run better (more reliably, consistently, etc.) it's short, suppressed ARs, which Eugene Stoner probably didn't quite have in mind. Piston-uppered guns with adjustable gas, even more so.

 

[Art Eatman]

I just really don't want to see a bunch of squabbling and fussing over this difference in designs. This horse is already right at being dead, dead, dead. Y'all just really don't want to join that horse.

 

[Tirod]

Where ever the piston is placed brings with it it's own specific issues. How those are compared is actually a weighing of what advantages and disadvantages each has, and how a user will prioritize them.

Some prefer one over the other because of what they actually do, others bring in anecdotal history that is actually unrelated, or overemphasize a disadvantage that isn't a significant factor. And some others are furthering a marketing advantage that deliberately plays off the buying public's lack of education on the subject.

All I intend here is to point out that there is actually little reason to create an oppositional discussion, because it's not really DI vs. Piston - BOTH have a piston, gas rings, a cylinder, discharge ports, and cycle the action. It's really about whether it uses a operating rod from a different location, or not.

If that fits better, as suppressor users have suggested it does, then by all means use it. If not, ok. What the buyer wants is some clear cut information. With that in hand, they make their own choices.

I've range fired and cleaned the M2, M9, M16, Mk17, M60, M249, and M1911A1, my personal HK91, Remingon 700, Glock 19C, Ruger LCP, and Winchester 94. They all get dirty actions, recoil, gas operated, or blowback alike. There's no free lunch, and misinformaton abounds. Be careful about what you want to get, it's like voting, you get the Congress you deserve.

Might not be what you had in mind.

 

[BrocLuno]

I vote for electric action - al la the Mini Gun

 

[Jaws]

There's a distinctive difference in what most people call DI and gas piston setup.
Where the hot smoke goes after it cycled the action.

--- In DI it is "vented" in the middle of the rifle, that is best kept clean, cool and lubricated.
--- In a piston system the hot smoke is vented out of the rifle in the gas cylinder area, wich in most rifles is in front, on top of the barrel away from the guts of the rifle.

The area that is being pushed by the hot gases to cycle the action gets hot in both systems, but the difference is what else will heat up more than is needed.

Here is a good example of heat reading in few different rifles after four mags loaded with 28 rounds rapid fire:


From here:
http://www.m4carbine.net/showthread.php?t=62889

As you can see they all get hot in the gas block area, but there's a distinctive difference between the other areas of the firearms.
The DI rifle in this test clearly run hotter than the other systems.

The dirty, hot gas that vents inside the DI rifle has a clear negative effect. This is not just internet hype.

 

[HorseSoldier]

If there is one thing that piston-uppered guns tend to run better (more reliably, consistently, etc.) it's short, suppressed ARs, which Eugene Stoner probably didn't quite have in mind. Piston-uppered guns with adjustable gas, even more so.

It's not so much that pistons run better at short barrel lengths, it's that when we talk about shorter barreled DI guns we're really talking about modifications of the original 20" AR gas system (and ammunition developed for it) to shorter and shorter barrel lengths and pushing further and further outside the design parameters of the original AR-15/M16 (but not DI operating systems more generally). If someone took a blank slate approach to designing a DI carbine with a 10" barrel it wouldn't be any special trouble to make it work.

 

[Bartholomew Roberts]

As you can see they all get hot in the gas block area, but there's a distinctive difference between the other areas of the firearms.
The DI rifle in this test clearly run hotter than the other systems.

The dirty, hot gas that vents inside the DI rifle has a clear negative effect. This is not just internet hype.

I'm sorry Jaws, I appreciate the information you are taking the time to share with us; but that is an underpants gnome conclusion you've reached.

You've shown that the DI is hotter in several areas; but you haven't shown how the temperature difference has a clear negative effect. I'd agree it is an interesting hypothesis that deserves a further look; but you haven't brought it out of the realm of internet hype just yet.

Given that even after four rapid fire mags, most of the parts where there is a significant difference are still less than 200F, I question how much of a negative effect that is going to have on 8620 steel or Carpenter 158 steel. 200F seems well within the comfort zone of either product.

 

[Tirod]

Interesting link, I've read others using temp guns that show the carriers are less than 50 degrees different. There's more than one source of temp studies out there, and the results should be easy to repeat.

In DI it is "vented" in the middle of the rifle, that is best kept clean, cool and lubricated.

There are two assumptions here: 1) Gas is vented in the middle of the rifle. The majority of the high pressure hot gas is vented out the two discharge holes located on the side of the bolt carrier facing the ejection port. It's released in the first portion of the cycle. After the action opens, gas also flows past the cartridge brass. All self loading actions do that- you get residue on the bolt and case as evidence, regardless of recoil, gas, or blowback. When the carrier has finally separated from the gas key, some low pressure gas exits blowing down the cam pin channel. The total amount isn't that much. 2) Clean, cool and lubricated isn't a combat weapon standard. The performance requires running dirty, hot, and lacking lubrication. What designers do is compensate by building in relief and clearance so that debris and residue don't affect cycling during the normal operation of the gun. Mean failure rate analysis determines the maintenance schedule. Soldiers cleaning their weapon daily have no issues with gas residue - it's environmental debris that is much more prevalent. Mike Panone demonstrated that by firing a weapon to stoppage stripped of lubrication and not cleaning it. It took over 2,400 rounds, more than ten combat loads to do it. Thats why gas residue has little basis in the final analysis.

What we see here is weighing known issues and elevating them to being objectionable, when in reality, they aren't that important. Examining the bolt tail of an extensively fired AR will show deposits, compare that to a barrel mounted piston gun, and you will find deposits. Whether either are a cause for stoppage is entirely different - as Garand owners will tell you. Ignore the gas cylinder on those, you will pay a gunsmith to separate them. They have to be cleaned repeatedly, just like the AR.

That's where the problem lies, having points in context to determine their actual rate of causing a problem. No problem with wanting to avoid stoppages and jams, but magazines and ammo are the primary causes. If more users would focus on the #1 gun stopper, cheap bent GI mags, there would be more young soldiers alive today. It's why DI vs. anything is a farce - all of them still use the same mag and mag well, which is a much bigger problem.

Focus on what actually stops the gun when you need it, and where the piston winds up becomes almost unimportant. Each has it's advantages and disadvantages.

 

[C-grunt]

Colt has already shown that heat will destroy a barrel on a M4 and the gas tube on a M4A1 before anything happens to the BCG.

 

[Tirod]

Those tests apparently were documentation that the M203 cuts don't really belong on M4 barrels, among other things, and they have been deleted on the latest version.

I'm waiting to see a similar video where the gas piston is mounted on the barrel and it's shot to destruction. The only difference would be at what number magazine it happens. It's not really a much of a test of anything.