Haganah - TMT IV Sten markings

[Peter Laidler]

Armourers and the designers will say that there really is no such thing as API. All API is, is simply a coincidental by-product of a breech block having a fixed firing pin set within a recessed bolt-head. Nothing more or less! And you MUST have a recessed bolt head otherwise the base of the round would foul the protruding striker as it was sliding across the breech face while being centred and fed into the chamber. I wrote a long article detailing the technicalities of this for the forum several years ago.

Blow-back is a more accurate description I feel but others say that the operation of blow-back is really just another form of piston operation. The spent case operates as a piston for several milliseconds