Originally Posted by
jmart
I'm tracking with everything you're saying. But I do have a question, and it's based on my following description/assumptions of the breakdown of the extraction cycle. Maybe I've got it wrong, if so, please correct.
Primer ignites, bullet releases from case mouth and travels down bore.
Bullet passes port and charges gas system, sending gas to BCG via gas tube.
Gas is trapped within a volumed defined by the gas rings, which are part of the bolt. the carrier surrounds this, but is not impacted directly by gas pressure, since it's trapped within the volume bounded at the rear end by the gas rings (which aren't moving, see paragraph below), and unbounded fwd from the key, to the gas tube, to the barrel port, and out to the muzzle -- it's all open going fwd.
Bolt at this instance can't rotate or move to rear because bolt is engaged against lugs. Even if casehead thrust acts on bolt face, trying to push it to the erar, the bolt won't budge as long as it's locked up against the barrel extension lugs. I can envision once the bolt is unlocked, then the entire BCG, as a unit, can travel rearward, but I can't picture how the carrier moves initially rearward for the straight portion of the cam pin slot you mention. Assuming the bolt remains locked and pressure isn't acting on it in the rearward direction (maybe radially between the area/void forward of the rings and against the interior walls of the carrier, but not rearward), I can't picture how the carrier moves rearward that initial bit before the cam pin rides the angled slot and unlocks the bolt.