partner,
Most gas stations and tire centers will gladly give you wheelweights for free. Just tell them what your intentions are, and maybe offering a cold drink, can go a long way towards a great free scrounge relationship.
I use straight WW, and water quench them, to harden. This method nets a BHN of 19-21, pretty hard, as cast bullets are concerned. Have driven them in excess of 2700 fps, without leading, and good accuracy. Never had the need to alloy with other metals.
Jeff
After heat treating, did you immediately quench the bullets in cool water ? This is the key to hardening cast bullets.