Some years ago, when I was doing a lot of bullet casting, I read an article in an NRA publication on heat treating of cast bullets. In essence, it said that a very small percentage of arsenic in the alloy was necessary to be able to heat treat cast bullets, and that the wheel weights of that time contained sufficient arsenic. I ran some tests and proved to myself that heat treating worked, using a SAECO lead hardness tester for my comparisons. Unfortunately, the effect is not permanent as hardness decreases with time. If lead shot contains sufficient arsenic and antimony it can be easily hardened in a home oven just like the bullets.
