I've looked thoroughly through my T&T Handbook and the only bullet that seems close is #22, the .40 LeMat. I've read this was a French manufacture for the CS and was in production until 1865. If it is indeed a .40 LeMat then I have a greater predicament because I found it at the Indian Wars site I have permission for that was in use from 1865-1870. How do you think it could've ended up there? Souvenir from the CW? Some post-CW soldier using a revolver captured from the CW? Former CW soldier who transferred to the US Army? The measurements are .417 dia (at the widest location), .645 length and 157 gr weight.