True bear pepper spray in a proper holster is likely the most accessible and effective protection you can have. Getting a rifle on target quickly would, I think, be a challenge unless you are already holding it at the ready. A high power revolver would be likely quicker but harder to get on target such that a charging grizzly is "put down."
I've carried when fishing in back country, for protection against cougar, black bear, and any two-legged critters that might hassle me. But if I ever go into grizzly country, I'm taking the spray.