I'm not sure I buy that, a piston gun is generally much better than impingement. You can package a piston up in something that looks nearly identical to the AR15 but it's not the same as the original firearm. Also 5.56 isn't a great caliber for military purposes, on one side the lack of immediate stopping power of FMJ and on the other over-penetration in close quarters without frangible.
There is no statistical evidence that pistons are more reliable. Indeed, ARs with pistons are less reliable on average (although this is mostly because the AR bolt carrier / receiver interface is not designed with that in mind, and carrier tilt results if you try to adapt it).
Not using a piston has two advantages. First, it's lighter in general, and in particular, there's less reciprocating mass, which means that weapon is easier to control, especially in full auto. Second, the recoil impulse in Stoner's design goes directly back along the bore axis (which is why it doesn't have carrier tilt!), whereas pistons add an angular component, which translates to more muzzle flip.
The disadvantage is that you get carbon deposits in the action. But the effect is usually overstated - there were numerous tests with uncleaned ARs firing several thousand rounds without any ill effects from the carbon - it just keeps running so long as you keep lubricating it. According to Armalite, most of the deposits are in places where they don't matter, and where they do matter, the action itself is designed to remove much of them as it cycles.
I'm not surprised - obviously, the longer you go, the higher percentage of them will fail, and that's true for AK and others just as much. I'm specifically addressing the myth that because of the Stoner action depositing more carbon inside the receiver, you must clean AR much more often than other assault rifles, and that it will fail quickly if you do not.
So these experiments show that carbon accumulation is not the issue. There are other things about AR design that make it less reliable in some cases (and more reliable in others, like that infamous mud test), but they apply to both DI and piston ARs.
>piston gun is generally much better than impingement
Hello 2008, my old friend.
I’ve done high speed and thermal camera testing on AR firearms. There is no honest advantage of what you are calling piston guns over DI, which is a short piston on the carrier itself. There are good and bad examples of both, piston AR pattern guns have carrier tilt, extra weight, more parts, more required maintenance, and get just as dirty esp when suppressed as DI guns.
It’s an old opinion you have there. I lived through piston-mania 2008. DI effectively won when you look at anything remotely considering retrofit designs.
>a piston gun is generally much better than impingement.
The AR-15 is a piston gun, though: the piston is the bolt itself (the bolt carrier acts as its cylinder walls- this is the reason why the back of the bolt has piston rings). And because said piston is right in the center of the moving parts, you don't have to worry about those parts rotating off their axis (i.e. there's no force tilting them up or down)- the only reason the receiver needs to be there is to hold the barrel on.
This doesn't work for barrel lengths below about 10.5"; at that point an external piston system is indeed more reliable. Also, because the gas tube is a weak point in terms of heat dissipation, the internal piston AR isn't the best choice for sustained automatic fire- but in that case you just give one squad member an external piston gun much like how the Russians distributed their beefed-up AKs.
Logistics is your force multiplier. Sacrificing the (excessive) performance of 7.62 to improve the rounds you can field is well worth it. That said, 5.56 still holds up well in CQB, provided you have a sufficiently long barrel and a bullet with decent ballistics. But therein lies the problem. The move to shorter barrels means lower muzzle velocity which severely gimps a round that leans on velocity for its lethality. The move to shorter barrels has also necessitated the move to piston-operated guns like the HK416, but they don't come without negatives, especially when guys are over-gassing out of fear of stoppages.
