".....I suppose starting with about 90 grains of 3031,,,,,"
Oh please dont use 3031; very very sensitive to small variations in charge and is known to give unexpected pressure excursions in large Nitro Express cases. Back in the Elmer Keith & Jack Lott days it was thought to be equal to Cordite in burn rate and so was used until some guns accidentally were ruined.
Better to try RL15 or H4831 and starting loads for the .500 Jeff from the Woodleigh manual.
Use Fed 215 primers...... & a backer rod filler with RL15
- Mike