Hrm, odd. I can't seem to find the stack of 10x18mm ammo, and I got all the parts active :S
EDIT: Also Flak Cannon! :D Very awesome
DoubleEDIT: Apparently the fact that 10x18mm exists on one gun is a bug actually. It's present on the Classic MP and nothing else.
TripleEDIT: And yes, the Pepperbox can cause crashing, even on hosting servers, so it's not just single player D: