RL-22 is THE powder for the 300 win mag with 180-200g bullets. Work up to 75g RL-22 w/180g bullet, you and your rifle will love the results, guarunteed!! This combo has shot under 1 MOA in about 5 different 300 WM"s I've played with, and they all shot around 3050-3100fps. Sure puts the thump on elk!!
I shot my first spike elk at 525 yards with 180g Nosler Partition out of my Ruger Stainless/synthetic 300 Win mag. 1 shot through his shoulders and he was tumbling down the canyon like the earth was yanked out from underneath him. I can still remember that day like it was yesterday, even though it was close to 10 years ago!!