When it comes to a large bear stopper, the absolute minimum would be a hot loaded .357 Magnum cartridge with 180 grain hardcast bullet and large/flat meplat. (And at least a 4-inch barrel, with a 6-inch barrel being even better for a modest velocity boost.) Another possible absolute minimum would be a hot loaded 10mm Auto cartridge with 200 grain hardcast bullet and a large/flat meplat. (Also with at least a 4.5-inch barrel and 5-inch barrel being even better for a tiny velocity boost.) And I think both of those are not adequate to stop a large bear reliably.

I am a serious adherent to the philosophy, “There is no replacement for displacement.” My woods gun (for smaller black bears and white-tailed deer) is a large .44 Magnum revolver with 6-inch barrel and moderate loads with 240 grain softpoints. If I am worried about large bears, then I step up to hot loads with 300 grain hardcast bullets and large/flat meplats. Those have a muzzle velocity around 1,350 feet-per-second out of a 6-inch barrel. Note that those 300 grain .43 caliber bullets are 1.5 times the frontal surface area and twice the weight of those 9mm +P+ 147 grain penetrator cartridges.

Anyway, in bear country, I would carry a 10mm with defensive rounds. But the only time I go into bear country is when I go to the Rod and Gun club. And bears do not like all of that noise.