Period correct '74 Sharps Buffalo Rifles?

[Distant Thunder]

You don't need any special loads for deep penetration with the .45-70. You just need to push a 400 to 500 grain bullet at 1200 to 1600 fps. You can get into that range with BP or very easily with smokeless. A good hard cast round nose bullet will travel straight and penetrate a long ways. They are actually hard to stop and a catcher's mitt isn't going to do it!