As dkf notes, depends on what the babbit is. A good place to start would be 2-1, pure to babbit & see how it casts & shoots. Obviously, you want to blend in a smaller test batch, like 4-6#. Add more pure if it seems too hard, go to 1-1 if it seems too soft.
I haven't found many handgun applications where straight clip ww alloy doesn't do a fine job as a bullet alloy. The 357sig/357mag running hard might be an exception.
"Given adequate penetration, a larger diameter bullet will have an edge in wounding effectiveness. It will damage a blood vessel the smaller projectile barely misses. The larger permanent cavity may lead to faster blood loss. Although such an edge clearly exists, its significance cannot be quantified".
Last edited by fredj338; 04-20-2013 at 00:31..