Pure lead minnies are a must, sized .001-.002 undersize to the bore diameter. I'm of the opinion that even a small amount of tin will make casting easier but hurt accuracy. Case in point. I shoot a Hoyt relined original 1842 rifled musket with a bore .687. I shoot a .686 pure lead minie. The musket is a tack driver. I had the occcasion to use some lead shielding from a jobsite to cast some minies. Supposedly it was pure. First off, the recoil from the first shot was noticeably less than normal. Fouling about 6" ahead of the breech was bad and accuracy was not nearly as good. I couldn't figure out the problem until I tested the lead. Soft, but not pure. I went back to my original stash of pure lead and everything retuned to normal.
Muskets with a slow twist( 1/72, etc.) can shoot roundballs very well, but if it has progressive depth rifling, a thick fiber cushion wad may be needed to take uo the windage in the deep grooves at the breechend while allowing a patched ball to be started at the muzzle where the grooves are only around .005. For hunting, at normal woods ranges. I prefer the minie in my .69s and .58s. They are accurate, hard hitting, and much faster to reload if you need too. While I have had success with prbs,
I've never liked the thin metal ramrod for running a ball home, especially in a hurry.
Duane