Head on, if the shot goes up the nose, a 22 lr will likely get the job done. Bella Twin shot it through the eye, then shot it 7 more times.
http://www.bear-hunting.com/2022/7/grizzly-with-a-22-c It is a good reminder that if you can, slow the hell down. It is possible that most head shots just miss the brain being fired in hast.
Though, I don't want what can work some of the time, I want what will work most of the time. I hope to never fire a 22 remfire at a bear.
Also, a 700+ pound bear was killed on Kodiak with a folding buck knife and fists. I still don't cound my pocket knife as bear protection, but if push comes to shove I will try it.
Side note, while the same species, costal browns are larger than grizzlies. Not sure if a 26 5/16 (bella twins skull) would be meaningfully different from a 30 12/16th (record brown), probably not, both are big.