I've never owned a 300 mag so i can't comment on that caliber. I own a 30.06 and a 25.06 and if i were to hunt big bears, moose or elk i would choose the 30.06 over the 25.06 because of the heavier bullets that it offers. For deer i use the 25.06 exclusively and have for years and have killed countless deer with it and imo it just doesn't get any better than the 25.06 for deer.