Prior to the 80's I hunted with the 30/30 Winchester '94 that I inherited from my father. I downed several grizzlies and elk (all under 100 yds.) with that rifle. I was later able to afford a Winchester 70 bolt-action .30-06. I harvested several rather large grizzlies and elk with that caliber from slightly greater distances, as well.
Approximately seven years ago, I purchased a .300 Weatherby Magnum. This cartridged rifle is a very powerful one indeed. It is also quite accurate, once you've adjusted for recoil.
I really do believe that the .30 caliber cartridge is really the universal round for all North American game, from varmints to grizzly and polar bears. Anything above .30 caliber, I feel, is overkill!
So what do you guys think?