What can you tell me about this upper?

[cneider]

I have this 9mm upper that Dad brought home from WWII. The story was that he was only allowed to bring home one pistol and 2 rifles. He brought home an Artillery Model Luger and this upper, plus a VZ24 and a G33/40. Serial numbers on the extractor and toggle don't match the receiver and barrel. What does the "42" mean? It's not stamped "DWM" like my Artillery Model.

There are some proof stamps on the right side, forward, but I can't capture them with this camera.

I want to slip it on my Commercial Model Alphabet Series P08 (.30 Luger) when I want to fire 9mm with that frame.