There is no real big secret to lead alloys. Unfortunately wheel weights won't cut it. I am always getting approached with cheap lead and alloys, in the long run it just isn't worth it. If you want to cast what we cast our bulk lead is it.The purity of lead is not as important to accuracy as it is to barrel life. It is very important to keep elements like Calcium out of the mix. The only way to do this is to have assayed materials. The Antimony is another important part of the mix that is all most impossible to properly mix with lead in a DIY situation.