I would suggest you use RTV.RUBBER MOLD MAT..I have flipping and swim jig molds made of it and they have poured 4 to 5 hundred heads each and still ready for more. I've made a lot of these molds to get my own style of heads that I want. (RTV will show all defects) First before you get ready to make your mold take your jig you want and look it over real careful for defects and any thing else that isn't quite what you want. You can take play doe our clay that kids play with and fill holes our add to the jig. Now that you have your jig the way you want it, take and coat the jig with a LIGHT coat of D2T. This will give you a very nice finished (smooth) blank to pour in to. If possible always make two molds of the same copied head. Because of the heat from the lead will make the mold very hot and that is what will destroy the mold. What it does is slows you down and one mold has some time to cool down. Another hint is to be sure to make the mold thick enough. At least 3/4 to 1 inch thick on the widest point on your jig.Will make it last a very long time. When you cut your sprue hole cut it on the back side of where the hook comes out. You only have to cut one side of the mold for this. THE POURING HOLE CAN BE AS BIG AT THE TOP AS YOU WANT ,BUT WHERE IT ENTER THE MOLD MAKE IT VERY SMALL .You can always go bigger but never smaller. Good luck and I hope this helps. STEVE