Black Bear , or Brown Bear, Kodiak, or Polar Bear ?
I think it makes a difference.
IF any of the later 3 , I"m with ... trip, or knock your GF down and run, and don't stop running.
I've been researching, discussing and cussing this subject for a while.....
Generally speaking .. the consensus I've gotten out of people who have been around them is :
1. Black Bear; a well loaded .357 round 'can' kill them. Myself, that's a Buffalo Bore 180 gr round with velocity of 1851 fps and approx 1181 lbs energy. But, a .44 or bigger helps.
2. A 30-30 rifle or above.
3. Brown Bear ..... BIG, BIG , and Bigger if at all possible. 454 Casull or .50 cal.
4. Polar Bear ...... a really good rifle, great aim and lots of distance.
My use is ... worse case a Black Bear, and more likely wolves, cougars, or a very aggressive coyote. I've had closer contact with all of these than I would have liked and was "hunted" and tracked by wolves and cougars. Wolves are usually just more curious, unless very hungry, in a pack, and want to steal the food you have around you and are willing to fight you for it, or you threaten them. I was able to discourage them. Coyotes, wolves and cougars, all have thinner skin / tissue, not as much muscle mass and not as thick of a skull as bears (all a reason for more need of good penetration on a bear).
I'm sure I"m not saying anything you don't already know... but , in my case... I'm capable of shooting faster, more, and more accurately with a stout .357 load than a .44, so that's what I'm going with. It should meet most of my needs, if needed.... which would be a close range negative encounter where speed, accuracy and quanitity are needed.
In camp; I'll have a 30-30 or 30-06 for my use.