My M11/9 with the Lage upper would eat most anything. It cycles well suppressed with 147 grain flat point ammo.
I had problems with PPU ammo firing out of battery, leaving a bulge near the rim. It must be soft primers.
I've removed numerous 1940's primers from .50 cases. Shoved them out very slowly. Anvils were deformed on some. I had fun hitting the primers with a hammer.
Tempering would have solved the problem. I was told that this guy took the receivers 'across the street' to Ramo for riveting. I can't believe that Ramo would have riveted the trunnion/ sideplates out of square. In my opinion, the guy was a crook. I still need to get the trunnion re-riveted.
I have one. Bought it around 1988. Sent it to Class Three Supply in Tennessee for assembly with a parts kit. They said the heat treated end was brittle and welded on another end. When I received the gun, I never got it to work correctly. The trunnion is visibly not square with the side plates. That has nothing to do with the side plate. I still have the gun. I won't mention the NOS parts I sent down that wasn't installed on the gun and I never got back.