Originally Posted by CHW2021
Don't even bother looking to change anything in the gun unless you have a large quantity of the ammo, it is the depth of the primer seating causing the problem. I have run into this a few times shooting surplus, that ammo may work perfectly well in another gun and not yours. Primers may well be in spec for whatever contract they were made under, maybe the rounds will run a garand well....who knows.
Do check that the rounds are non-corrosive so you can clean properly.
Got it! The ammo was originally Machinegun linked ammo.