Wow. An interesting and confusing thread.
As to bears, lets get real: In a true shtf scenario, there would at a minimum be hundreds of thousands of armed people, roaming every conceivable corner of the lower 48, desperately seeking one thing: food. Within a few months, all large game, including the large bears, will have been hunted to the brink of practical extinction. By the end of the 19th century, the grizzly was pushed to the brink of extinction in the lower 48 by folks armed primarly with the .45-70, .38-55 and finally the .30-30. If a shtf situation occurred, and you saw a grizzly, you would not be saying "Oh no, a grizzly!" You would be saying, "Oh boy, a grizzly! Meat!"
Folks who worry about "death by grizzly" in these fantasy situations are a real puzzlement. Yes, there is some extremely remote chance of getting killed by a grizzly, but there is probably a 100 times greater chance of dying from dysentary, exposure, cholera, diptheria, influenza, pneumonia, tuberculosis, or malnutrion. These were the mega killers of the 18th and 19th centuries on the frontier, . . . not bears.
As far as an all around rifle round, it is my understanding that in Alaska, among the native people, one of the most common survival rounds is the .223. They use it for practically everything, and this is in a place where small, medium, large and mega large animals abound.