As shooter had said, you don't "need" that much power at 300 yet. But power is still nice. If you want you can use a 416 rem mag. Lots of guys use a 300 win mag or a 7 rem mag. Anything bigger is definately unecessary IMHO. Where do you hunt? if it is heavily populated you will definately want to stick with a small mag or a standard cartidge. Anything from 25-26, 260, 7-08, 270, 280, 3006.... any will be fine.