I started with leather in my GPR rifle because that's what I thought folks used. I then tried lead after reading about that idea, so I flattened out a round ball, and that worked equally as well, so that's what's in there now. I have since tried lead on a Pendrsoli Kentucky pistol and it really didn't like that lead wrap.... my flints kept breaking down. I switched to leather and a smaller width flint and seem to have no more problems. Could have been the leather or the different flint size, but I tend to think it was the leather just because of the mechanics of it all. I'm sticking with leather on the pistol, and will probably switch back to leather on the rifle too, given all that I have read here.