Happened to meet an old family friend living in Unaka, North Carolina perhaps 45 years ago. Hw was living back in the woods, WAY off the beaten path.
He went to walk through his apple orchard and check on his hives, and pulled out his .22 rifle in case he saw a rabbit. A medium-sized black bear started following him; not charging, but not leaving either. He climbed an apple tree, (which wasn't very high) to put space between him and the bear.
The bear came to the tree and began acting as if he was going to climb, standing on the back legs and raking the tree with his front paws.
The old fellow waited until the bear turned his head and placed a shot right through the ear hole, and the bear dropped and rolled downhill. He put 15 more shots into the head and body (all that he had left) but the bear never moved after the first shot. He had the hide pegged out on the side of his barn to dry when we visited, otherwise we may have never known about that story.
So Yes, any caliber can kill, BUT.... we aren't going to see an ear shot with a charging animal. I have read some writers who were stalked (as opposed to a brutal initial charge) who were thus prepared a bit and found some type of shelter to slow down the brunt of the charge and force the animal to at least approach them cleanly and openly. They were able to get in 2-3 decent shots based on having time to calm down before shooting. I can't imagine the stress of a sudden charge in the open with no retreat or shelter. I would guess that hits would be a low percentage unless it was a very experienced person; even then, the sudden action has to throw off anyone at least a little bit.
Interesting side note: A friend was deer hunting from the base of a tree, just propped up against the trunk for comfort so he could watch two trails.
He heard a noise, looked left and saw a bear that appeared to be stalking him. His thought later was that the bear saw his movement but didn't equate him to a human. He only had a rifle, but didn't want to shoot the bear or scare off any nearby dear. He moved around, waved his arms and finally stood up to scare off the bear, but realized that the bear had managed to get too close for comfort by stalking. He made sure that he had his Ruger revolver in a chest holster whenever he went out again. The next year, he was sitting in the same area and hears the same noise to his right this time, so he simply grabs the revolver and cocks it as he draws, then turns & points in one motion. He told me later, " Did you ever point a Magnum in the face of a game Warden? Well , I sure have!" He said they both must have been scared by the outcome, but he felt that the Warden got the worse end of the deal.