I would never hunt a grizzly.. not enough of them.
But if I did, I'd bring a big BIG gun... I wouldn't even think of going after one of these things with anything less than a .308.. I'd take a .50 BMG if I owned one.
I took these photos myself during a camping trip with my wife.. Slept with a double barrel 12ga, and my AR10 next to both of us...
These things scare the hell out of me.. shear size alone is awesome!
Pictures taken at about 50 yards..