CBG hit the nail on the head. In 1865 Erskine S. Allin invented a method to convert the 1863 Springfield rifle musket (muzzle loader) into a breech loader. The initial loading for this gun was the .50-70 cartridge. The original cartridges were a copper case, 70 grains of black powder, under a 450 grain bullet. From 1865 to '68 Frankford arsenal produced inside bar primed cartridges. The inside bar primed case was crimped just above the rim to hold the primer in the case. I believe your case is a Martin primed copper case, because the crimp holding the primer cup in place internally looks like it goes around the entire case, while a Bennet primed case the crimp is interupted, but in the same location as the crimp on yours. So your case dates after 1868, and it doesn't have a head stamp, but Frankford Arsenal, as far as I know, was the only one making an inside primed, copper cased cartridge at that time, so then, your cartridge dates after 68 but before 1873, when Frankford Arsenal quit loading the 50-70. The army adopted the 1873 Springfield rifle and that gun is 45-70 caliber, which was the gun Custer's troops were armed with in 1876. The Allin conversion 50-70 is the one the army used to whip Red Cloud at the Wagon Box Fight. Red Cloud had not come up against breech loaders before that fight. Even though the 50-70 was dropped by the army, Sharps still made a rifle for that cartridge, and there were a lot of buffalo slaughtered with the 50-70 cartridge early on. I think Buffalo Bill was using a 50-70, if I'm wrong, I'm sure someone will correct me.
This is the Allin conversion of the '63 rifled musket.
Loaded 50-70 cartridges. Far left is bar primed. Next is Bennet primed the other three are reloadable brass case cartridges.
