Sure looks like a 50-70 to me. Your measurements tell the tale. Back when Red Cloud was working over the army very badly at Fort Fetterman, in Wyoming, the troops were issued the 50-70 Springfield, and at the wagon box fight the soldiers armed with those single shot, breech loading rifles defeated Red Cloud. Before that, they were armed with muzzle loaders, and Red Cloud was feeding them their lunch. You would think that the inside primed cartridges wouldn't be reloadable, but the Indians got around that by punching a hole in the back of the case, large enough for a cap that would be used on a cap lock rifle or pistol, and dropping a small rock in the case, then filling with powder and topping off by seating a bullet. The rock kept the primer from being pushed into the case without going off. Sounds crude, but it worked, so the army issued an order to smash all the empty cartridges so they couldn't be used over. In my collection, I have a found 50-70 case with a hole punched in it for a primer. The army used the 50-70 from 1866 until 1873, after which, they became surplus, and were sold to civilians, and probably traded to the Indians as well, either legally or illegally. Anyhow, the Indians acquired firearms one way or another. Sitting Bull certainly had Custer out gunned with repeaters while Custer's troops had the single shot Springfields.
