I am using a bottom pouring pot and I am holding the mold tight against the pot thinking the same thing, that the lead was cooling down. Didn't help any. The only place that I am getting a void is the backside of the hook no place else. I am going to try pre-heating the hooks the next time I pour and see if that helps. I am pouring in a building that I keep the heat off when I am not using it. With temps around 0, I sure the hooks are cold and cooling the lead down before it gets into this tight area. Thanks.