I bought a bunch of hard lead on Ebay, and a .568 mould from Jeff Tanner to cast balls to shoot out of my Colt musket. Wasn't sure how it would work, but the hard lead balls group as well as as the .570 swaged. I patch 'em tight and swab between shots. Just my experience. I don't see why a patched ball has to be pure lead. If you can shoot a patched brass ball accurately, as some have done here, I don't why stainless steel wouldn't work. It's the fit between the patch and the rifleing that imparts spin to the ball. Everything else being equal, the only thing that might affect accuracy might be the density of the ball. Just my opinion.