I'd find what shoots best, and a 1 gun, 1 bullet load for all game I'd plan to hunt with that .300 win.mag.

usually I think 180gr and 300win.mag. is THE combo! but find what works...there are some quality 165gr bullets out there, even some 150gr, but I think I'd want something in the 165-200gr bullet size for elk etc... which then could also be used on deer.