Mea culpa, mea culpa, mea culpa!
I would have thought of 41 magnum as a starting point.
And that’s not unreasonable. Neither is it unreasonable to consider 10mm a starting point. When faced with small amounts of reliable data (as here), large amounts of flying BS —<ahem>, in/around an arena where emotions, impressions, desires, and tightly-held beliefs are often resorted to before rational thought, it’s not always easy to determine the perimeter of “reasonable”. Thus, this sort of developing bruin-haha. It becomes a pick-your-poison sort of affair, really.
It’s clear that at least sometimes as disparaged cartridge (e.g., 9mm, let’s say) can
help get the job done, even with a brown bear. It’s also clear that sometimes an old stand-by (such as .357 Mag) can “fail”—for examples, see the ammoland article referenced above. It actually is interesting reading.
I said “
help get the job done”, and used quotation marks to denote “fail” because of something too often noted, then ignored: the firearm is only part of the response to a charging/attacking bear. There are many other things that come into play, including, of course, defensive-fire skills, the ability to remain cool under pressure, simple physical abilities, manner of carry and accessibility of firearm, presence of other deterrents/weapons, presence of other animals, such as horses or dogs, presence of other people (and the skills and on-hand equipment of those people), time of day/daylight, weather, terrain, and, yes, even luck.
So, choose carefully whom you listen to, think well about what they say, and then proceed. Recognizing that even the best plans may “fail”, at least occasionally. I can’t recall which famous general said that battle plans don’t survive intact beyond first contact with the enemy, but I mention it because there’s an important truth there. Napoleon may have been history’s greatest general. Or maybe it was Alexander. Or maybe Clausewitz. Or...it doesn’t really matter. None of them went undefeated.