9x19 in 7,63x25 chamber

[alvin]

Thanks for the input, but I would reserve a little on the "worn parts" theory. It's hard to explain why some Mausers that lost almost all rifling still have straight edges behind the bolt stop, and some guns with excellent bore and much lower mileage have bent/deformed edges. I feel that the latter was still more related with firing higher pressure ammo.

Have not gotten a chance to inspect a damaged gun for detail yet. Will find one.

If the edge behind the bolt stop is very bent (like the 2nd pix above), the bolt cannot close completely. I just did a little experiment. By inserting a tiny cleaning patch between the bolt and the receiver, I created a gap of around 1m/m between them. Then, pushed down the trigger, the hammer did not fall.... the trigger had been disconnected from the sear. So, the gun shown in the 2nd pix is not functional anymore.