40 Short and Weak
I have to agree a 40 Short & Weak (as it is called by 10mm nuts around the world) is not what i would consider an adequate bear gun. All I have to say is that Ranger friend is damm lucky he was able to get head shots and neck shots. Those are the types of shots that are luck and not easily executed under stress. I won't carry anything less than my 41 magnum into the woods if I think I will tangle with a bear. Heck last year a guy died in Alaska after emptying his 357 magnum into a Grizzly. Now granted there are differences between Black Bear, Brown Bear, and Grizzly. But I would look at the hunting regulations for good guidelines. Here in Colorado any pistol you hunt with has to have 550 ft/lbs of energy at 50 yds.
357 mag has 448 ft/lbs at 50 yds with a 170 grain bullet
40 has 413 ft/lbs at 50 yds with a 155 grain bullet
10mm has 452 ft/lbs at 50 yds with a 180 grain bullet.
41 mag has 630 ft/lbs at 50 yds with a 210 grain bullet
44 mag has
839 ft/lbs at 50 yds with a 240 grain bullet
454 Casull has
1470 ft/lbs at 50 yds with a 260 grain bullet.
The above figures come from online charts available from Speer, Remington and Winchester ammo.
So if it were me and I had to pack heat in bear country and my life was really important to me this is the gun to carry.
Alaskan
Chambered in 454 casull it is really a beast but keep in mind you can shoot 45 colt in it too, which are really mild in comparision on 330 Ft/lbs of energy at 50 yards.
I am sorry to say full auto or not .223 Remington is really only good at killing things that weigh 60 pounds or less. I don't care if it is our Military round intended to wound people weighing from 100 to 200 pounds. Plus if it is full auto it is not allowed for hunting so it would no go over well at all if it were used in defense in bear country.
Ask the Colordo PD they used their issue AR-15s to take out some Buffalo that got lose in town it took over 120 rounds to kill 3 buffalo from around 10 to 15 yards!!!!!
Sorry for the rant but I just didn't want some one here to run out and buy a 9mm, 40, or 45 to defend against Bear attacks and get hurt thinking they were truely carrying big bear medicine. A true bear size gun starts at a 44 magnum. Yep that is right all I have is a 41 magnum but I can't buy a 44 or the Alaskan so it is what I carry, keeping in mind any gun on my hip is better than none. So choose wisely and know what kind of power you are carrying Bears are a lot thicker skinned and tougher than we are.
Tim