FYI, an optimal load in a 10mm creates 750 lb/ft of muzzle energy. My 500mag develops 3100 lb/ft. Your choice.
I've had the opportunity to shoot a few bears with a shotgun. Nuisance black bears. News flash, a 12ga does not kill the bear or even make it crumble to the ground. They usually turn and run off. The same shot with a big bullet? Lights out. Big brown bears are hard to kill when you're out hunting to kill one. Get one pissed off and trying to kill me? No shotgun will get my vote.
News flash for you, Stewart: I've seen one shot kills by 12 gauge shotgun on both black bears and Brown bears. NOT EVERY ONE, FOR SURE, BUT GOOD SHOT PLACEMENT, AND/or rapid reload and fire works.
One black bear boar killed by a young lady who worked for me, and had never fired a gun before she went to work for us. She weighed 85 pounds, and that 870 about knocked her off her feet when she pulled the trigger. Brenneke slugs work well, but placement is always an issue. I wouldn't have wanted to piss off that young lady bad enough to encourage a gunfight....
I've killed two black bears with a shotgun, and they work.
Given the the choice, for brown bears, I'd use something heavier, but a pump action shotgun cycles really fast, and with Brenneckes, they hit hard. Most folks shoot pretty naturally with a pump shotgun.
if it's a bolt action, better plan a one shot kill. There are people who can reload fast with a bolt action, but they're rare and they shoot them a LOT. Brown bears are tough, no doubt. Again, shot placement is essential. Only one I've had to shoot was with a 458, which I didn't like, but it's what I was given.
As noted by AKTango, the 12 gauge offers lots of options: cracker shells, bear bangers, plastic bullets, slugs, and burd shot for a ptarmigan.......rapid reload and large capacity magazines.
whats not to like? Get some good slugs and practice. Our crews (and me)carried them in bear country day in and day out, and LIVED in country so thick with bears you saw bears every day.
And, we hardly ever had to shoot a bear.
MTV