Here is some interesting reading, that might (or might not ;>) be relevant to the never-ending 'Caliber Wars':
Handgun or Pistol Against Bear Attacks 104 cases, 97% Effective
As I've noted in the past, it's probably best to just carry whatever suits your own circumstances!
Thank you for this link, and I went down most of it. It is very interesting in detailing occurances with man and a bear and usually a gun. But I did not find it too enlightening on caliber, knock down power, and safety. Even the .22 had a good record! But here are the things that are clear from this account telling:
1) You MUST hit the object (in \all h=of these cases, the bear), and not just shoot it in the air or miss. I was surprised to see that with the .357 Mag, one instance was a 'failure'. This was because he never hit the bear! so, the heading for each caliber is a bit misleading. The .357 Mag has well over double the power of a 9mm, although with almost any caliber, that would depend on the actual loads.
2) The actual loads are not discussed anywhere. This is particularly important with non 9mm loads since all the other calibers have power ratings that vary greatly, sometimes varying 3-4 times the power of a similar low end caliber round. The 9mm caliber is fairly consistent om its power.
3) ALL the 4xx calibers were 100% successful. But again, the term 'successful' in this list can also be misleading. But in most cases, the 4xx round killed the bear on the scene. But with lesser powered ammo, such as the 9mm and the .45ACP, it took many shots to get the bear to leave or die.
4) Some of the reports used the term 'pistol' when they really means handgun, and the gun was probably a revolver. Revolvers are not pistols, in spite of what you see in the movies, and on a lot of the ammo sites. So, in these cases, the caliber was a bit ambiguous, other than the category it was listed in.
5) There is a big difference between a female Black bear, a male Black bear, a female Grizzly, and a male Grizzly. But all of these occurrences with the various bears are lumped together, within the caliber with which they were shot. I really can't see anyone using a 9mm or a .45ACP or a 40mm on a big male Grizzly.
And I would like to thank the_leper_colony for the link. It was very interesting, especailly with all the black bear attacks, which I thought were suppose to be quite docile and run from humans all the time.
But I have to reiterate my comments above about the 9mm and M-16 'pea shooters' in a military situation. In this sort of situation, you want one shot too take down the assailant or target, and for them to not shoot back. This happened in WW II and Korea with the M1 and the BAR, and even the Tommy gun, and early on in the Vietnam with the M-14, which shot .308 rounds. The BAR was absolutely devestaing, and was completely different from the mass shooting you get from the full auto fire of the M-16., as it tore up everything it was fired at. The 1911 used the .45ACP round, and it did the same thing in close, although I do not know the exact load they used in the military back then. Today, our guys on the ground are defintely at an unwarranted disadvantage, shooting against AK-47's everywhere.