Here in Alaska, the natives almost exclusively use .223's for all their hunting. The Ruger mini 14 being the favored rifle.
They take caribou which go up into the 600 pound range and moose which go...1800 pounds?
My elderly neighbor, a Koniag, took many brown bears with his fathers .25/35 Winchester and countless deer, seals and sea lions.
These bears here in Kodiak are massive. 2000 pound boars have been weighed in and 1500 pounders are taken every year.
I asked him how in hell he killed Brown Bears with a .25/35.
He told me you had to sneak up close (30 yards) and then circle till he got your wind. A browny will normally stand on his hind legs when he smells a man and growl or "woof", He would wait for the mouth to open and then shoot into the roof of the bears mouth.
He was absolutely serious about this and I was amazed. I said something like "Christ Hank, what if you miss?" and he replied "Oh, you DON'T want to miss!".
Another neighbor, also a native has hunted deer here on Kodiak with a .22 mag pistol since the late 60's. He never misses. He goes out at mid-day and stalks them to their bed and shoots them between the eyes.
Its about skill, not calibers.
The Bears and Bear Maulings Page: members.xoom.com/keithrogan