COPPER !! Yes, I said copper ( Cu ). Not pure copper, but around 1% also Arsenic ( As ) we need around 0.5% for the ability to heat-treat bullets for increased hardness.
Those percentages are in the finished alloy.
So I'd suggest a "finished" bullet alloy similar to the Lyman #2 with the copper and arsenic.
Also an "alloying package" with ingots designed to make better bullets from wheel weights or even straight lead.
A sort of "babbit" of 50% Tin, 20% Lead, 20% Antimony, 8% Copper and 2% Arsenic. Would that work?