The shot will make fairly soft bullets, good for low vel. target loads, not much harder then the swaged lead bullets sold by Speer and others. Adding tin will make them much easier to cast up, better flow, fillout, etc. but won't add much to hardness. Mixing with wheelweights will harden then up somewhat, you can them heat treat them for some hardness or better still, find some very hard compositions or Linotype/monotype. Quenching and heat treating will harden them but if left to sit for long they will revert back to their orig. hardness. If you cast 'em, load 'em, and use them within a reasonable time, you should be good. Remember that in most handgun and hunting applications, very hard cast bullets are a negative factor, you should match bullet hardness to the velocity you want and/or the game you are shooting. Bullet fit in the chamber/barrel is more important then bullet hardness, both, against leading and for accuracy.