You need to be careful when making up greatly reduced loads for large-volume rounds. Ignition can become erratic and dependent on cartridge position. There are powders that have lower density than the usual made for doing this. I have some SR4759 but I don't know if it's still made or not. I know that Trail Boss is made to replace black powder in cartridges and is "fluffy" but I don't know if it's nasty like Pyrodex or clean burning.
VIAS muzzle brake (pronounced VASE), makes a 300 Win Mag feel like a 308!
I'm dealing with a shoulder issue and am changing to a decelerator pad and adding either lead or a C&H mercury reducer. Specific to brakes, what are the recommendations? Thanks