1. Find some suitably sized stones. 2. Forget melting lead - I guess your young - Instead get some plaster (the stuff they use for fixing cracks in walls. Mix it up and put some into 2 hollow boxes. Press marbles or something round into the plaster half way on both boxes. When dry you have a mould. - Grease the plaster well to stop the next stage sticking - Fill each mould with either more plaster or cement- When dry you have a half round ball - Stick 2 together to make your ball. 3 Faster to use the marbles..