[Travis McGee]

I didn't know you could shoot .40S&W out of a 10mm barrel in a semi. Don't they headspace on the neck rim of the brass?

(PS, I just wish I got to shoot enough to answer some of these questions myself, drat it!!!)

[P8riot]

I didn't know you could shoot .40S&W out of a 10mm barrel in a semi. Don't they headspace on the neck rim of the brass?

That is correct. I should've added that .40SW shouldn't be fired through an auto pistol chambered for 10mm as a matter of practice, but in an emergency (and only an emergency) I've heard that it can be done (but I never have). It is never smart to use ammo that is different from what the pistol is chambered for. The S&W 610 revolver is different as it uses full or half moon clips and "headspaces" on the rim.

(PS, I just wish I got to shoot enough to answer some of these questions myself, drat it!!!)

I never get to shoot enough.