I have a 338 rum being built. Plan is to use dbm and 300 smks. What powders give low fill % to allow room to seat the 300 smk to mag length and not have a VERY compressed load?
RL33 will give you excellent performance in the 338 RUM but will definitely fill up the case. I have see 2840 fps with a 300 gr SMK loaded at mag length 3.690 with it. That's in a 26 inch barrel !