There was also another incident in which an attacking brown bear was killed in Alaska with .45 acp.
It took 18 rounds before the bear dropped. I would probably go with a .454 Casull.
There have been incidents were grizzlies were killed with 9mm, .40s, and even .22. I would rather have a .338, but you use what you have with you when it is needed.
Mr. GG2 carried a .454 Casul the whole time he lived in Alaska.