Bob,
I beleive Daryl has it backwards as to alloy of lead/tin vs lead/ antimony.
If I need a fatter bullet from the same mould I use an alloy that has more antimony in it.
Tin can only harden an alloy so much. I use up to 5% tin and once that point is reached I start adding antimony.
In my experience, linotype will produce the largest bullet from a mould.
Hope this helps.