I was being cornered by a mountain lion once on top of a bare desert mountain top in Southern New Mexico , near the Mexican border. All I had on me at the time was a hunting knife. I may have lost the fight.... but the dang mtn lion would have not come out of it clean and uninjured. I would have put up a good fight.
But, I would have preferred having a good caliber handgun on me.
A .22LR beats a sharp stick, but I'd go down to maybe .32ACP at the least preferring to stay .380 and above. The smallest I carry now is .38/9mm.
38 spcl followed by 9 x 19. EDC is 45 acp.
No smaller than a 38 special ,,,,, but I do have 22, 22mag, 25, & 32 which I would
used if push came to shove,,,,, and I feel if they were well placed,,,, would do the
job,,,, just slower to take effect.
there's really no need to go with anything smaller then.380,especially when you have pistols as small as the lcp to slip in your front pocket..
Although the .40 is the smallest caliber of gun that I own, I'd prefer a 9mm as the minimum.
From the tests I have seen (for example, at GoldenLoki) the minimum handgun caliber that will reach the FBI penetration minimum of 12 inches with FMJ ammo is the .32 ACP. That said, given that the .380 is available in guns that are the same size as the .32 versions, my personal minimum is .380 with FMJ ammo.
Of course, I will echo the general sentiment that I can make a .22 work, and would much prefer a .22 to a knife, bare hands, or a rock.
Personally I'd trust any. As it is better than none. I trust pepper spray, a knife or 2, or whatever I can get my hands on. I generally carry 9 mm and or .38+p. But as others have said will take anything over nothing. I was pretty deadly with a .177 crossman bb gun as a kid on my parents farm.