I thought cannon balls were made in "shot towers".
I think that's what they were called. Been awhile since I read about them in a high school physics textbook.
Basically a tower built so that when a cannon ball or musket ball was still semi-molten it could be dropped down the tower into a barrel of water. On the way down the ball of metal would cool and have a uniform density due to the free fall. If it cooled sitting in a mold then heavier material would settle to the bottom and produce a cannon ball that wouldn't straight and kill those damn redcoats!