Haven't tried it, but will an AR hammer follow the bolt home when released if the trigger is held back?
Should not, but if the sear surfaces are worn, the hammer will follow. That was a common issue early in the NM AR15 experimentation phase. Before the good triggers came out, the first I remember was the
Milazzo-Krieger trigger, shooters would stone the issue trigger to a short crisp pull, and the things always failed at some point in the future. Then the shooter would have a double in a rapid fire stage.
That Milazzo Kreiger trigger always in time failed too. You can go to the link, there is a sear engagement adjustment screw, and no matter what thread locking compound you use, the screw gets loose, and then the rifle starts doubling. I much prefer the two stage trigger mechanism that came on my Armalite NM AR15. No adjustments once the trigger is set up. Simple is far better.
I don't really consider mechanical failures as true "slamfire" events, even though the rifle did fire without the shooter pulling the trigger. I prefer to refer to slamfires as events caused by the inertial impact of a firing pin on a sensitive primer. However, broken parts or not, the outcome is the same.
The FN49 has a high number of reports of rifles blown up due to out of battery incidents. Such as
I always thought these were caused by the inertial impact of a free floating firing pin. You look at a FN49 firing pin, it is big. However, until I purchased a FN49 book, I did not know about the one piece firing pin problems the rifle had. The early versions had a one piece firing pin that would bend or break in the firing pin channel, and with the firing pin sticking out of the bolt face, the affect is identical to an advanced ignition system, such as the STEN. So I don't know if the out of battery incidents are due to broken firing pins or sensitive primers.
I do want to comment on the AR15 design. Yes Stoner designed a bolt where the firing is completely blocked from moving forward until the bolt lugs have rotated into battery. Therefore you would think that an out of battery slamfire is impossible, and I did. Well, never say never. They happen in the things.
I never took into account bolt bounce and a slight delay to primer ignition. What happens is the bolt lugs rotate close, the firing pin rebounds off the primer, the primer slowly ignites while the carrier bounces back, which unlocks the bolt. And then, an out of battery even happens.
A shooting bud of mine who was a Security Guard at a National Laboratory that has Nuclear materials and shoot on sight zones, told hm he witnessed an out of battery event with a military M4 and Federal Gold Medal match ammunition. These guys get to practice with Federal Gold Medal Match!, Uncle Sam has deep pockets. Anyway, the out of battery slamfire incident with an AR15 mechanism is extremely rare, rarer than inbattery incidents by far, but they happen.
There is one rifle I have not found any slamfire events, and that is the HK91 roller bolt rifle. The firing pin is positively blocked from going forward by the design of the bolt
the center piece has to push the rollers out into the locking recesses for the firing pin to reach the primer. And the firing pin spring is extremely stiff, I think you could use them as automotive valve springs.
But, of course, never say never. These rifles are not as ubiquitous as AR's, and if they were, maybe I would hear of an inbattery or out of battery slamfire with the HK91
'
If the fourth round was high primered, there could have been a three round burst.
