Have any of the people here ever bought salvaged range lead? The times that I obtained it it was a mess, mixed copper and lead, maybe a fourth rimfire, packed full of sawdust, and basically big flat wads about the size of a plate. I broke it into useable pieces, and melted it in lots that I mixed as well as I could, cast it into small nights, and then randomly used everything from that pile of bricks. Not terribly hard, didn't cast that well, either, but it worked pretty well when I just added a pound or two into the pot as I worked with better metals.
Cores aren't meant for casting, and rimfire bullets are far too soft.