I can't get them to cast as well as I like with out adding a lot of tin. If I'm going to add tin its going to be to pure lead, since I have several hundred pounds of it. Wheel weights work good for some of my other uses that pure lead ain't good for.
All my pure lead has been free also, check with plumbers that do remoldeling, roofers and folks who work in bridge fab plants. In fact I have better luck getting free lead than wheel weights.