Just use 80% Alliants load data for the 125 GDHP
(ie: 20% less than 5.7 grains) as 5.7 is the MAX.
So around 4.5 to 4.6 grains
10% less for start load and another 10% because you have lead and not jacketed (actually you can use jacketed data for lead but that's another story and you are just starting.)
Alliant Powder - Reloader's Guide