There is a secondary reason that the bump in the slide causes the trigger bar to disengage the sear loop from the sear. Not only does this allow the sear to raise up, to catch the striker (cocking the striker), but it allows the gun to function as designed, as a semi-automatic action. The trigger must be released, to allow the sear loop to reset under the sear. After the reset, the trigger must be pulled again to allow the gun to fire. Without this disengaging of the sear, it is possible the gun could become full auto. The gun could continue to fire as long as the trigger is pulled. It is not a certainty that full auto would be the result. It could allow an even more dangerous situation, as it could allow the cartridge to fire before being fully seated in the chamber.
Even though the striker is retracted from the bolt face, by the striker spring, after firing, it is possibly that the striker could move forward and strike the primer, upon the slide slamming the cartridge into the chamber. This would be more likely with "soft primer" ammunition.
Full auto is possible if the striker is not retained by the sear, and the trigger remains in the rearward position (bypassing the striker safety/blocker). When the forward movement of the slide pushes the next new cartridge into the chamber, and then the slide slams closed, the forward inertia could cause the striker to move forward and strike the primer. If it strikes the primer hard enough, it would fire, and would continue to fire, until the trigger is released or the ammunition is exhausted.
This is a possibility. Would this happen? There are many variables that would have to be just right, to allow this to occur. What I have described is not how a full auto gun is designed. The full auto gun allows the action of the gun to close/lock, and the striker/hammer is fully cocked. Just as the action closes, an arm/lever (auto sear) then releases the striker/hammer. The gun continues to fire as long as the trigger is pulled or the ammunition is exhausted.
I have a SlideFire stock on my AR10. It works almost exactly as a full auto gun, except there is no auto sear. The sliding stock allows the trigger to move back (recoil) and forward (pushing forward on the handguard) into a stationary trigger finger, which acts like the auto sear. I put a compensator on it, to keep the barrel down, and tame the recoil. Lots of fun shooting, but very expensive. I don't auto fire often, or for long periods of time. Even though my AR has a heavy barrel, it gets very hot, after firing only one full mag (20 rounds of .308/7.62). I don't want to warp my barrel.
Bob
