I have never owned a .300 ultramag but have owned a couple of .338 win mags and taken lots of moose as well as smaller game with them. The .338 is just about ideal for the heavy stuff like moose and elk. With proper bullets it just plain rips right through animals no matter what it encounters. If I was hunting Alaska regardless of wether I had a grizzly tag or not, its what I would carry. Even if your not hunting the big bears they could be hunting you and your kill.