flippinfool. I use high temp silicone in some of my molds. It works great and I could'nt do without it. I even put the silicone in direct contact with the molten metal with no problems. However, I do not use lead but Bismuth Tin. Pouring temp is probably no more than 250-300°C (heat setting 4 on lee pot). You should have no problems using silicone away from the cavity. Fill the cavity, wait until the surface just starts to dry up and then press down a hook (easier to remove hook if surface's a bit dry first).