I believe hardness would probably be around 16 bhn, maybe some over that, but the only way to know would be to use a hardness tester. It has been too long since I've used that mix and water quenched, for me to remember exact.
I'm presuming your reason for mixing half pure lead is because you have it or it's more available than wheel weights. If so, you have a very valid reason, or if you want to make good expanding rifle bullets it is impossible to beat ww diluted with pure lead until water dropping or oven heat treating, depending one which method you want to use, produces a hardness of 16 bhn or slightly less. That hardness with very low antimony content is the only way I've been able to make 'hard' lead bullets expand. The antimony content of straight ww is high enough that 16 bhn or harder bullets crumble rather than expand on game.
Casting temperature has nothing to do with bullet hardness when water quenching. Temperature when they leave the mold determins how hard they will be. Best temperature, or highest practical temperature is had by watching the sprue very closely as it hardens. A few seconds after it solidifies you'll see a color change, a dullling. Knock the sprue immediately and drop your bullets quickly after. If you cut sprues at this temperature you won't have problems with lead smearing on the bottom of the sprue plate either.
