A lot of the responses were for hunting scenarios, which is quite different than self-defense rifle shooting. I believe I could kill any bear with a .243 in hunting situations with the shot being one of choice and the bear not knowing where I am; change that to a charging bear with my address, now I have a completely different story, and nothing less than a .45 of some sort will do!
In a charge situation I want the bear to go all gooey and loose, NOW!