Grizzly and brown bears are one and the same from a scientific standpoint. It’s just that the coastal brown bear lives an easier life and over the years has evolved into a bigger bear. Based on weights, a grizzly is about twice as big as a black bear, and a brown is three times as big. Polar bears are about the same as the brown bear in weight.
All these bears share a common bond in that they are North America’s only true dangerous big game. They have the ability, disposition, tools and willingness to kill you. It would serve you well to keep that in mind when selecting a rifle to hunt the big bears.
From the standpoint of what to shoot them with, we can consider these bears as all alike. They are big, tough, nasty tempered and hard to kill. If you hunt them, it will be expensive, and it’s unlikely that you will ever do much of it in your lifetime. You owe it to yourself and to the bear to show up well equipped.
The minimum gun suggested in most texts is a .300 magnum with 200 - grain bullets. I don’t know about you, but if I were facing 1,000 pounds of raging teeth and claws, .30 caliber would seem pretty puny no matter what the bullet weight.
A .338 Win. Mag. with 250 - grain bullets seems like a more prudent minimum to my thinking. Better still, consider the .340 Wthby Mag., .338 - 378 Wthby Mag. or .338 Rem. Ultra Mag. The .375 H&H Mag. with 270 - to 300 - grain bullets seems about right, and the .378 Wthby Mag. doesn’t look like too much gun to me. Any of the .416 rifles with 400 - grain bullets would make decent shooters for big bears.
While many guides carry .458 Win., it’s not really a bear - hunting cartridge. Guides usually don’t bring their rifles into action until things have turned sour. That means they aren’t shooting until the bear is too close. When you are hunting, it’s foolish to shoot at a bear that’s a long way away from you, but with a good rifle a 250 - yard shot is reasonable. The .458 Win. is not really a 250 - yard gun.