Starting a STEN Mk V SBR in the US

[17thairborne]

Advance primer ignition doesn't really fire outside the chamber. In theory maybe, but the cartridge is actually fully seated and the bolt is the only thing still moving forward. That way it takes more pressure to move it back, keeping things closed longer...in theory. People picture a cartridge firing while on it's forward trip and that's just not what happens. It has to bottom out first. I know what the SAIC instructors taught us, but it just wasn't quite right...

Makes sense what you say regarding the STEN with fixed firing pin firing from an open breech block. In this case there is a point where as the block with round stripped from the mag moves forward into the chamber on the barrel, the pressure of seating the round is sufficient to cause primer ignition. With any slight changes in the chamber caused by dirt or powder residue, or problems with the round, it would seem possible that slightly higher friction between the round and the chamber would be imparted onto the fixed firing pin, and premature primer ignition could occur before the round is sufficiently seated to contain peak pressure caused by powder ignition.

With a closed bolt system, it seems reasonable to conclude that the round would be fully seated before the hammer strikes the firing pin. I would assume premature ignition in the closed bolt system is eliminated if the trigger is not allowed to function until the bolt reaches the closed position. Is that correct?