Either the .45 or .50 cal. would be my choice. With paper patched bullets and black powder, pure lead bullets can be used to good advantage, or 50/50 Wheelweights and pure lead makes a good alloy as well. With grooved bullets, .001" to .003" over groove diameter, straight wheelweights work well for me in both calibres, using SPG, Lyman BP lube or 60/40 Beeswax/vaseline.