A 12 gauge auto or pump with rifled slugs or 00 buck is the best remedy for a charging grizzly, unless you have a 45-70 cal rifle ready.With the auto 12 you can triple tap and that stops them dead. Usually it turns them to the side and then you can get to the tender parts with follow up shots.
You need significant penetration to pass through the hide and get to internal organs; lead shot or slugs MIGHT do it, but DDupleks steel slugs are 100% sure thing-- my anti-bear loadout.