Never use car battery lead, ever. Casting, like most other skills is best learned through experience. Casting is very forgiving. If the projectile is not what you want, throw it back into the pot and try again. Pre heat the mold for best results, either the pot itself or a warming plate work fine. Alloys are fickle, a temp gauge is your best guide. When you get good results, note the temp of the lead and atmospheric temperature. I find casting to be very rewarding. There is a learning curve. Flux your alloy, wear your protective gear. It’s a very simple process.