Hello from England. I'm having some trouble navigating the forum as some of the terms used are unfamiliar. I make and supply ball moulds in brass and aluminium. Smallest.25" and largest 4.5". The latter for a mortar. I am thinking of making a mould for hollow hemispheres so that two could be joined to make a hollow ball. This would reduce pressure and save a lot of bullet material. Any feedback would be gratefuly recieved.