[mrerick]

The 9mm cartridge headspaces on the mouth of the case.

If the chamber were cut deeper for a 9x21, you would see the cartridge drop deeper into the chamber than it would on a 9x19 chamber.

The Italians specifically prohibited 9x19 chambers in civilian guns so that you could not use the military ammo.

Attempting to fire a 9x19 cartridge in a 9x21 chamber could be a rather dangerous experience, especially if the primer were struck enough to set it off. 2mm of excess headspace would lead to head separations and possible damage. You owe it to yourself to verify this barrel's actual chamber depth.

The way to verify all this for sure is to use a set of headspace gauges. The breech should not close on a field gauge.

Marc