My experience has been that different rifles like different loads, different makers and different bullet weights.’
You may have to spend some time and money finding the one your gun likes, or it might like the first thing you run through it.
Small things can make a difference. For years, my .270 liked 150 grain stuff, almost any 150 shot better than any 130. Then I bedded it into a new stock and now it likes 130s best. It also now prefers the cheapest ammo over the expensive stuff. (go figure)
My .338 shoots almost everything OK, but it loves Barns “Vortex” 210s.
Like Mkoutr said “ Plan your bullet for the largest game the rifle may take” .
Pick a few factory loads that will do anything you might want the gun to do, and try them.
For a .300 WSM I would try;
Federal Premium Partitions and Trophy Bonded in 180 grain, and Barns Vortex 165 grain. Any of these will work well on any North American game, and 90% of anything else in the world.