For what it's worth, for a .450-400 3" I use two loads with a 400-grain Woodleigh soft nose: 80 grains of IMR 4831 if the old rifle was proved for 55 grains of cordite and 83 grains if proved for 60 grains of cordite. Large rifle magnum primer. 2-3 grains less if shooting a Woodleigh solid.