Quote Originally Posted by Hoosier View Post
So it's just the force of the gas pushing back on the BCG that causes it to unlock, then I can see how both systems works pretty much the same. Why does DI need the gas to actually enter the bolt carrier instead of just acting on the face, like piston?

The other common method for rifles, other than piston or DI, is roller delayed blowback, like the H&K G36, ja?

Thanks for the schooling, and the video is helpful too.

H.
As far as the gas entering the carrier it acts as an expansion chamber, allowing chamber pressure to drop to a safe level before unlocking the bolt. It also is doing the same thing as a piston, hence the gas rings on the bolt. You have to contain the gas somehow, otherwise the pressure drop will not cycle the action.
With a piston rifle this "buffering" is accomplished by venting a certain amount of gas off before the piston.

You also have weapons systems that operate purely off of recoil, the 1919 and M2 come to mind.