I'm jealous of you guys that have a source for isotope cores. Their alloy makes a good boolit and they were probably the cleanest lead that I ever smelted. They were clean enough that I only used wax to flux. But, I lost my source for them years ago.
Wheel weights are still available here where I live. They are often dirty, greasy, painted, coated, mixed with junk and require sorting. Just about everything bad thats been said about them is true. But I've smelted a bunch of them. I hand sort all of mine. They have always made a good boolit for me. Occasionally I'll add a small percentage of tin to the pot but not very often.
It looks like range scrap is going to be the source in the future. That has its challenges too.