On that topic:
12 bore round ball on buffalo - I just don't know. If the gun shot well with a huge load, way over what Pedersoli maxes it at, and with a hardened ball - likely, imho, for broadside shots.
Yes - hard (alloyed) or hardened WW or hardened "cast from shot" balls are capable of being shot in a muzzleloader. Hardened slugs cannot be shot accurately in one, pure lead only.

I'm thinking my single English Sporting rifle in .69, with a patched 15 bore (.677") hard ball would suffice - but, it's only a single shot with no fast second shot can be had. It takes 8 to 10
seconds to re-load, using paper ctgs & the .682" hardened ball.