If I were going to try a Muzzle loader I would want a 450-535 grain bullet. You don't need a lot of velocity with bullets of that weight range. I believe Bryan Pierce shot through the two Cape buffalo with a 435 Grain Corbon. The shot went through a Bull first then went through a cow and was recoered under the hide on the far side of the cow. Thats penetration. Many Cape buffalo have been taken with the 45-70 and Muzzle loaders.

Vince Lupo took the African Big Six with the Marlin Lever gun and Garret Hammer Head ammuntion.