Ok, this may get crazy / heated, but I am serious...
...going out into grizzly bear country with a AR 15 / M4, whether hunting, hiking or camping...and I know there are some folks way up north that kill large bears with .223's , even .22 Mags.
Now, these bears are a challenge no matter what you carry, but it is NOT necessarily the caliber, but more shot placement, staying as cool & collected given the circumstances, as possible...shot placement & a CNS hit, optimally, perhaps multiple hits as fast as possible so that AR with a really good-fast "SRT" trigger like the American Trigger AR Gold, may do the job?
I have M4's in 5.56 and the heavier side of "light" AR's, 6.8 SPC...
...the lighter side of "heavy", .300 ACC Blackout / Whisper and soon the heaviest .458 SOCOM.
6.8 SPC shoots flat, still light recoil, multiple fast placement vs.
.458 SOCOM (or middle-of-the-road .300 ACC) for frontal mass & energy, perhaps tougher to place CNS shots?
So what would you take out, there, 4 bear?