I personally suggest slightly harder than pure lead for large game, ie: bigger bears, moose and elk. a 50/50 mix of pure and the lead clamp-on weights would work. Do not put zink wheel weights in your lead pot.
Bear bones are quite light, but pack massive fat and muscle while a moose or elk leg, rib, blade or spine can badly flatten a soft ball and turn it away from it's intended lung or heart target. You need straight line penetration and on heavy game, a pure lead ball of light weight, might not work as expected.
Pure lead worked for us in the .69 and Brown Bess, but were badly flattened and woudn't exit on a moose. For this reason, I purchased slightly smaller mould (Tanner) so I could accurately shoot harder balls. In the .69, that meant a .677" ball (15 bore) for the .69 rifle (14 bore), for example.
The Bess already had a small enough ball for shooting WW alloys - .735" for the .774" bore. Taylor used a .030" patch in that one - yes, it was tight, but loaded nicely and gave pretty fine accuracy for no rifling. I once shot a 2 1/2" group with it at 50 yards - probably a fluke, but I was happy. That big gun seemed to handle round balls very well as long as the powder charge was decent.