AR 10 is heavy, maybe heavier than a pump shotgun... regardless, follow up shots on bear attacks are usally wishful thinking, one might get another opportunity to hit some fur, but I wouldn't call it a follow up shot.
I think a 10mm is a great option, if I didn't already have a 44, that's would be my choice
My AR10 is about a pound lighter than most--a DPMS GII Hunter.
Phil Shoemaker killed a brown bear boar by emptying an entire 9mm into the bear. I'm not a personal expert, but it seems like follow-up shots are possible in some instances.
