Have you had a 10mm fail to perform for you?
Yes. Not on a bear. On piece of cardboard. Failure to fire. A Glock. I've never carried a semi-auto pistol for bear protection. Never would except as the last resort.
I don't trust semi-auto anythings for bear protection. Know a guy that had a Remington semi-auto 30-06 jam after his first shot on a charging brown bear on Alaska's Kenai Peninsula. A big boar. After the boar crushed all the bones in his face, he stopped what certainly would have been his death by placing the muzzle of a S&W .44 Magnum revolver into the bear's brisket, and emptying it as quickly as possible. Firing by feel, while laying on his back with his face in the boar's jaws. He spent a week or so in the hospital, with his jaws wired shut to heal. Had significant plastic surgery - facial reconstruction. Actually came out of it looking pretty good. His face isn't quite as well balanced as it was prior to the mauling.
I've learned to recognize surviving Alaskan bear mauling victims by their facial scars and multiple hair parts due to the bear tearing through their scalps. Some look like they're wearing multiple hair pieces. I've met four different Alaskan's whose heads, faces, and scalps have been torn up during bear maulings. And seen pictures of more over the past 45 years.
When I carry a sidearm for BIG bear protection, it's a revolver. A 454 Casull or a 500 S&W.
While returning to recover the meat off of a downed game carcass, I'll carry my Remington 870 pump action shotgun, if I have it available.
I'd use an AR-15 if I was in a firefight with a bunch of gooks carrying semi-autos. Bears don't carry semi-autos. So my preference against a close quarters charging bear; 1) pump action shotgun, 2) heavy caliber bolt rifle. I only carry revolvers as bear protection for their convenience, like when walking out to the toitie in hunting camp, or walking the 1/2 mile to retrieve my mail. Would never go into a knowingly dangerous bear encounter with only a revolver.