Re: gas operation confusion
One point, the mechanism does NOT begin to move the instant the bullet passes the gas port. Assuming a piston system, the gas enters the gas port and flows into the gas cylinder. Then, due to its heat it begins to expand. It is that expansion in the gas cylinder that drives the piston, not the direct impact of the gas coming through the port. The direct gas from that small port does not have enough pressure to operate the piston and if it did, the piston would undergo a blow rather than a push. Note that some rifles (M14) use a gas cutoff and expansion system that proves this point; as soon as gas enters the gas cylinder, the gas port is cut off, and the action is operated solely by gas expansion. Also note that if the gas coming through the port were the operating factor, the action would stop when that gas pressure dropped, that is when the bullet left the barrel.
In a gas impingement system (AR-15), the gas must not only enter the tube but must exert pressure back to the bolt carrier before anything starts to happen; that takes even more time than gas pressure on a piston.
FWIW, while I am sure the action can be calculated, in practice, most gun designers have taken an empirical approach, in other words, try something and see what happens.
Last edited by Jim K; 04-05-2012 at 11:28 PM..