My experience is....soft as possible bullet with Black Powder...harder with smokeless, however, the hard bullet has to be a good fit in the bore for accuracy. i have not heard of a soft bullet leading(with proper fit) when using BP, smokeless is a diff. story. Expansion with soft bullets, at Bp velocities, has to be seen to be believed. In the days of the buffalo hunts, hunters wanted the big bullet to expand so that it was shaped "like a coin". It would stop at the far side,under the hide, and the hunter could reuse the lead. I have had Buffalo hit by a too hard a slug, just keep on feeding.