Do a ladder test with a good powder suitable for the 300wm. Lots of possibilities out there but for me I like IMR4831. Get on paper then put a big backer board and shoot your ladder at 300 yards. You will find out pretty quick where the sweet spot is.
In my 300WM 69 gr of IMR4831 behind 185 bergers is giving me 2" groups at 500 yards. ( this is out of a heavy Krieger barrel) but Tikkas are no slouch in the accuracy department.