I found a bit of info in an old McMaster-Carr hardware catalog that may come in handy.
The catalog states the alloy of the Lead and Babbitt hammer heads that they have for sale..
Lead Hammer Heads : 92% Lead
2% Tin
6% Antimony
Babbitt Hammer Heads : 95% Lead
5% Antimony
Hope this is of some use to someone......"Papa Jack "