This is particularly addressed to Smoke, though if anyone else has some
info please jump in.

I have a rimfire cartridge, around .40-.46 cal., somewhat bent. It has
a base that is crowned in the center, and appears to have been fired
from a weapon with a double firing pin. Can you tell me what kind of
weapon would have been used with this? I have been unable to find
reference to a double firing pin anywhere and cannot get the exact
caliber because of distortion.

Marty Pickands, New York State Museum