At long ranges the MOA grows, what was a one inch group at 100 yards at 1 MOA is a four inch group at 400 yards. Figure in wind, temperature and that the speed of bullets changes by manufacturer, the margin four error increases at longer ranges.
I went on the hunt for the perfect round for my .308, the rifle manufacturer recommended 165 grain at 2759 fps (I called and asked). pointed boat tail bullets. After trying many hundreds of rounds, I finally figured out the rifle manufacturer was right.
I'd start at 180 grain around 3000 fps, pointed boat tail. Then figure out which bullet type expands the way you want. The wrong bullet can tear up some meat.
Been my experience most rifles favor a certain food, and when you find it, stick with it.
IMO shoot what gives you the smallest group at a hundred yards, then memorize your up hill and down hill corrections, know your limits, around 300 for my .308, probably 350 for your 300 WM. Bullet drop happens fast after a bullets sweet spot, which I usually figure at a round 15 inches of drop.
Two old sayings that still apply, aim small miss small and most rifles shoot straighter than the shooter does.