You should prepare yourself for the onslaught of replies coming that will require you to buy fifteen different weights and brands of ammunition to find what shoots best in your rifle. And those replies are not wrong in what they're saying.
Buy a bunch of different stuff. Shoot groups and narrow down what shoots the best.
This can be time consuming, rough on the shoulder and especially rough on the wallet. Although if you just enjoy shooting and don't mind spending the money, it's the way to go.
The truth is that you can probably pick up any box of .300 win mag, sight your rifle in, and go out and shoot a deer at 300 yards. It's not rocket science. Sight in 2" high at 100, you're probably dropping 6-8" at 300. Do some practicing to confirm that and youre ready to kill deer.
Nobody can tell you what exactly will shoot best in your rifle though. Every barrel is different. It can be fun trying to find the best loads.
-Jake