Help needed with Bren mk II

[Brit plumber]

That does sound a bit suspect to me. My interpretation of slam fire is that somthing fires the round unitensionally, dirt, a bur, seized firing pin etc. So if your first shot was on trigger press (As expected) but then it continued to fire, surely this would mean that its still short stroking as the sear hasn't cought the breech block (Or hammer/ striker, what ever it is on a US semi conversion). So it still sounds to me like he has fixed one issue but that may be masking another.

[Peter Laidler]

Ah........ but to this Armourer, a slam fire is just another way of describing the Sten method of firing. As in close the breech, no locking and just fire the gun!

[Brian Dick]

Any ATF approved US semi-auto conversions must be to a closed bolt redesign. I'd guess it's a combination of both crap ammunition, (not enough gas), and friction from the semi-auto closed bolt design. A combination of some decent ammo, proper lubrication and turning the gas up a notch or two may well cure it.