No black bear on the planet cannot be killed with LESS gun than a .357. It's plenty, especially from a rifle. Buffalo Bore makes 180 grain loads that move into .30-30 territory. Black Bear have been taken with all sorts of weaker calibers. I don't think they've started wearing kevlar since the .44-40 ruled the west.
If you don't like .357, think it's weak (my own handload chronographs just shy of 1900 fps with a 158 SWC, a mildish load) go for a .45 Colt or .44 Magnum. We chonographed my 300 grain XTP Colt load I worked up for my Ruger out of my son-in-law's Rossi 92 at 1340 fps. That's enough for about anything, much less black bear.
Buffalo Bore gets as much out of an 18.5" barrel from a 180 grain load as I get out of a 20" barrel and a 158 grain load. My 180 handload shoots under 1700 fps. I'm not sure how they do it, but they do. 1850 fps for a 180 grain SWC is as deadly as any factory .30-30 170 grain load. Maybe the SD is a little low, but it would be no problem on medium game like black bear. Heck, my handloads would be no problem. I've killed three deer with it, one from the rifle, two from a 6.5 inch revolver. Bear ain't much harder to kill in hunting situations, not black bear, certainly no harder than a hog and lots of big hogs are killed with .357s, though I haven't done it, yet. I did, however, put down a wounded charging hog of about 200 lbs once with one shot from a 4" .357 revolver. I've carried a 4" revolver in bear country a lot day hiking and back packing. I have confidence in it. You gotta do your part, of course. A 600 nitro express ain't gonna do it with a miss.
5. 18.5 inch Marlin 1894
a. Item 19A/20-180gr. Hard Cast = 1851 fps
b. Item 19B/20-170gr. JHC = 1860 fps
c. Item 19C/20-158gr. Speer Uni Core = 2153 fps---- Can you believe this?!!!
d. Item 19D/20-125gr. Speer Uni Core = 2298 fps---- Or this?!!!