Originally Posted by
Arctic1
@Skullworks:
And why is that?
What is the difference between an op-rod pushing on the bolt carrier and the gas pushing on the bolt carrier when it comes to extraction? They both push the bolt carrier back, until the cam pin starts to move in the cam pin track, thus rotating the bolt until it unlocks.
There is no room inside the barrel extension for the gas to push the bolt forward. If there was, the gun would probably be unsafe to fire.
Both systems incur wear on the bolt lugs, as there will be a slight diagonal movement during unlock, where the bolt lugs on the bolt push against the bolt lugs in the extension. And case obturation has ceased by the time the bolt starts to extract the casing from the chamber.
Again, this is probably more related to bolt construction than DI vs piston. Also, like some of the guys with more expertise here said in previous posts, it is very hard to estimate bolt life. It will depend on how hard people run their guns, what kind of ammo they use, if the system is synced in terms of ammo, buffer weight and spring, what manufacturer made the bolt, etc.
Edit:
I just googled "Broken AR-15 bolts", and most of the pictures showed bolts that broke in two at the cam pin slot, and not sheared bolt lugs. Why they break in two in that specific area, I don't know.
We have never experienced that on our guns. The 10.5" guns have had some issues with broken disconnectors and sheard bolt lugs, during courses of fire shooting A LOT of ammo. If there is considerable carrier tilt in the 10.5" guns I don't know. I do know that the 16.5" guns are holding up well, and as a comparison, we see way more broken Aimpoints than guns.