Turk, I don't worry too much about pre-heating my molds whether they are cast iron (lyman), aluminium, or brass. I just set them on the edge of the pot, and when the alloy starts to melt, move them so they don't get molten lead cooked on. Start to pour bullets, and reject the first four or five castings. Keep rejecting them untill they start to look perfect, or at least the way you want them to look.
I have sometimes rejected as many as the first 10 -12 castings from a mold, especially if I have just cleaned and reconditioned it. Don't get discouraged. All the bullets you have just tried to cast that were not perfect, just drop back in the pot and keep pouring. One thing that you have to realize is that some of us are ladle pour guys, and then there are the new fangled types who bottom pour. It makes a big difference in the way you flux, the way you pour, even the way you hold your mold. So be sure to state which type of pot you are casting from when you pose a ? to the forum. Some of us will answer according to the way we cast, not thinking that you or others may be doing it differently. Merry CHRISTmas, Omaha.