Try a Lewis Lead Remover. JB Bore Cleaner will also work. I also recommend Bronze Brushes from Brownells as they are MUCH BETTER than the ones in blister packs in the LGS's or Big Box stores. For really tough crud, use a CHAMBER Brush in .357 instead of the Bore Brush. It is slightly larger and a little more aggressive on crud. Just note that the Chamber Brushes will not hold up as long as there is more pressure on the bristles, however they do work well.