In an interesting follow up to a post we made awhile back where Brandon Herrera was covering the parts of a fully-automatic AK and why some semi-auto AK’s still have full-auto sears inside them, Kalashnikov Concern tests whether an full auto AK will fire full auto with the sear removed.
It’s a quick video that that does an excellent job of showing just how intricate, and yet still simple and robust, the AK action is. Clever use of machined in geometry, something the Germans did with their roller-delay systems very well, make the AK’s order of operations cascade in time safely and securely round after round. The bolt, carrier, hammer, and sear all working together once the trigger is pressed and the selector has told the disconnector that it is unneeded at this point because the firer wants all the bullets.
Auto sears, like hammers, triggers, safeties, bolts, and carriers, come in different varieties but their purpose is the same. Only clear the firing mechanism for release when the weapon is in a safe-to-fire state in its operation cycle. The auto sear is the reason that “just filing down that one part” to make a weapon automatic instead just makes it runaway. Runaway guns will keep firing until they are out or they jam shut. Filed down guns are more likely to do the latter since auto sear systems are part of the proper timing of automatic fire.
The M16 and M4 are tripped by a proper dimension full-auto carrier interacting with the sear behind the trigger group. That sear is on the “third hole” and has its own spring and interactive surfaces with the selector switch. That is why ‘full-auto’ bolt carriers caused a kerfuffle a few years back since some thought they were “machine gun” parts and allowed full auto. Not quite, it was one of a series of parts and you need the whole series for it to work. But in the days when any legal advantage a company like Colt could take to distance the semi-auto rifles from full auto ones, they did. The results were goofy and unnecessary. No auto sear, not safe automatic. To say nothing of NFA penalties for making an auto through grinding or parts or any act without proper licensure.
Auto isn’t worth 10 years, and with todays ammo prices… auto isn’t that much fun.
So, can you ‘full-auto’ without an auto sear? Not in weapons where its part of the order of operations. On weapons where it isn’t, sure. The M249 does not have an auto sear because it is an open bolt belt fed, it has the single bolt carrier release control surface in its trigger. It fires once the bolt is locked based on the firing pin length and the bolt and carrier geometry. It doesn’t require an auto sear in its design because it is not working with semi-automatic parts (disconnector) to operate a hammer. The semi-auto adds a significant list of parts in the case of the 249 instead of subtracting a few.