ORIGINAL: Wingbone
I'm guessing 50/70. It was the first cartridge adopted by the army after the Civil War. It pre-dated the 45/70. Surplus military rifles were available to civilians after the gov't switched calibers.
I agree. 50/70, or a close relative thereof.......... It was used in the trapdoor Springfield that immediately preceded the 45/70 of the same basic design. If I am not mistaken, the cases were of copper, rather than brass...