I found an old Lyman cast bullet reloading book and used one of the recipes for the 420 grainer with a gas check. The book max was 47 grains of IMR 4198 for a velocity of 1932 fps, I used 45 grains and got 1935 fps. The 420's shot into an inch at 100 yds,they kick a bit more than the 40 grain load....not surprised there.