Yes, what Will Bison said. I just got finished using a sinker mold to cast fourteen 2 lb balls and it took just about a 2 1/2 gallon pail of wheel weights to do this. The aluminum mold gets mighty hot since each half of the mold is also the handle which is totally unprotected from the heat. I used a big C-clamp to get the molds to tighten up to avoid a lot of lead flowing out the bottom where the two halves join. Of course, I used thick leather gloves to handle the operation but the gloves were not enough protection from the massive heat produced by those molds. They stay HOT for a long long time too. These aluminum sinker molds are inexpensive but REAL cannon ball molds would certainly be worth their price. My 2 cents only. Blaster (Bob in So. CO)
P.S.... I leave the sprue on so I can easily lower it into my mortar and in the unlikely event of a mis-fire, could easily withdraw the ball by that intact sprue. Hope I don't ever have to resort to this though..