If I was going to inflict a .300 magnum upon myself, it would be of the H&H, Winchester, Weatherby persuasion, and I would not hesitate to use any of them on big bears with a decent bullet. Here's the thing though, the only advantage a .300 has over a .30/06 is trajectory, its still the same .30 caliber bullet that lands on target, so if I need more than a .30/06, I'd be looking at the larger frontal area and heavier bullet of a 9.3 or a .375, and neither would be as difficult to shoot as a .300 in a flyweight rifle.