George,
I have one of each. For some strange reason the post war Erma kit is too 'tight' (the rear knee joint is about 5mm above the receiver when breechblock meets the barrel). The excact oposite problem is with the was time conversion kit, then there is a gap between barrel and breechblock. But if I exchange the two barrels, they both get just right
(But then of course the numbers don't match up..)
Two things you can check;
-is the firing pin straight? These can easily bend, and if it's close to the frame the friction can slow it down.
-is there a gap between breechblock and barrel? Or perhaps it's too close?
Oh.. I'm missing two locking nuts btw. That reminds me to try my luck in the 'wanted' section in this forum again now.