I have used wheel weights to cast round ball for my 1858. They seem to work fine. But they say they are hardened to some degree by being alloyed with a small amount of tin and or antimonySo much misinformation regarding wheel weights and sailboat ballast.
I'll never understand the desire for people to steer others away from a free and highly usable material.
Soft lead is soft lead.
Whether it comes from Roto-Metals, a sailboat or the wheels of a '63 Beetle.