Agree with dolomite - try them at .311 first. It's more important to fill the throat than to match the groove diameter. I shoot very similar bullets to 2000+ fps in several .30 calibers using using IMR 3031 and Varget. If lower velocity is your goal, then almost any magnum pistol powder will be good. AA#9, Alliant 300MP, and 4100 are outstanding alternatives to 2400 for 1400-1600 fps loads. Blue Dot has given me amazingly consistent velocities in that range. Typical starting loads about 11 grains in the 300 Savage case.