Quote Originally Posted by tangolima View Post
Wow. I haven't seen information this detailed. Thanks.

I would say primary extraction happens when unlocking completes at about 2.3ms mark. End of piston motion means primary extraction completed and the bolt travels with the bcg at the same speed. That happens at 2.5ms mark. The displacement difference is about 0.8mm, or 0.031", or 1/32". Energy needed is 20*0.031=0.6 lbf-inch for brass and 9.3 lbf-inch for steel. You are right. My estimate was off by factor of 2.

Energy loss to extraction is indeed insignificant except for steel cased ammo. Looks like adjustable gas block is way to go.

-TL



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Nitpicky, but extraction starts at the end of piston motion (2.5 ms), when the cam pin bottoms out in the cam track. Only then does the bolt start to move.

What we have not taken into account is residual chamber pressure, depending on the timing of unlock there might be 200 psi residual chamber pressure. When the shoulder is uncorked from the chamber this will assist in extraction.

I normally ignore this as one, the force is low, and two, depending on the P-T curve used in the simulation, it sometimes isn't there.