Here are a few calibers that, when using heavy, hardcast lead or FMJ flat nose bullets at the absolute peak of their power range, in smaller firearms, are a decent compromise between being packable, and offering protection from 2-legged predators, and possible protection from 4-legged threats up to and including small to medium sized black bears (not brown):
• .357 Magnum
• 10mm
• .45 ACP
These 3 calibers can be found in many different guns weighing less than 40 oz., (which includes an all-steel full-size 1911). The heavier, more effective wildlife defense calibers such as .41 Magnum, .45 Colt, .44 Magnum, .454 Casull, etc. usually come in much larger and heavier firearms, and are usually considered "overkill" for self defense against human targets.
I have a 2.25" Ruger SP101, and the hottest ammo I can find for it is the Buffalo Bore 180-grain hardcast flat nose .357 that I have chrono'd from the 2.25" barrel at around 1,250 fps. I have no doubt in this round's lethality, but trying to quickly and accurately get 2 or 3 shots off from a snubby .357 with a very long and heavy double-action trigger pull is not very confidence-inspiring.
I also have an all-steel full-size S&W 1911 that I shoot very well, and the nastiest round I can find for it is the Buffalo Bore 255-grain hardcast flat nose that I've chrono'd at about 960 fps. from my 5" barrel. However, for some reason, Buffalo Bore seats this bullet very deeply in the case, and it causes it to nose dive and give feeding problems in my gun. I do want to try Buffalo Bore's 230-grain 45 ACP+P FMJ flat nose that they advertise at 981 fps. It looks like it would feed much better in a 1911.
The options in a 10mm are much more limited these days. If Glocks fit your hand well, then the 20 or 29 are excellent choices, with the 29 being much more packable, but losing a lot of the 10mm's potential due to a shorter barrel. Properly loaded to it's maximum potential, the 10mm can even top the .357, in a semi-auto with much higher capacity and faster follow up shots.
A concealed carry woods gun idea I've been considering lately is the Ruger SP101 loaded with 2 rounds of Buffalo Bore 180-grain hardcast flat nose .357, followed by 3 rounds of Speer 135-grain short-barrel .38 Special+P hollow points. This way, you have 2 potent rounds up first in case you meet a black bear that poses a definite threat, followed by 3 easily-controllable rounds for 2-legged threats.
If you want a handgun that would also be effective against brown bears, I wouldn't consider any of the above. If it were me, I'd want at least a heavy, all-steel .44 Magnum revolver with at least a 4" barrel. But now we're talking about guns that when loaded, weigh 3 pounds or more.
