7.62x54r Russian or 8x57 Mauser.
Both will need to be handloaded to reach their max potential but otherwise give up little to the .30-06. I still think the .30-06 is better all around, but splitting hairs.
If handloading isn’t in the cards I’d go for .308 Win.
The old military cartridges weren’t designed explicitly for hunting, but they’re so versatile. They have the power to put down a large beast, and mild enough recoil to ensure you’ll actually be able to practice with your hunting rifle and hit the animal in a good spot.
If we take bears and moose out of the equation I think one could do far worse than a 7mm-08.
The thing about .30-06 (and 8x57 and 7.62x54r) is that if someone said (in an alternate universe) “Hey, I just won a draw lottery for two -we’re going grizzly hunting. Flight leaves in 4 hours, come on!” I would feel like my rifle could unequivocally do the job. I wouldn’t be forced to think “Self, this is a once in a lifetime opportunity… shouldn’t you quick go down to the gun store and buy a (insert your favorite magnum cannon here.)” If I had a .30-30, I know perfectly well that hunters 110 years ago used it successfully… when it was just about the best thing going. But I’d feel quite under-gunned for anything larger than a big buck, and restricted to 150 yards or less. Which isn’t optimal for western big game. Virtually anything smaller than .30-06 would feel like not quite enough for a good margin of error, and most calibers over it would feel a bit ridiculous if the target is the much more likely deer, hog, or coyote.
