I had a close encounter of the black bear kind once in a campground in Seward Alaska.  I had nothing but a coffee cup.  But I did remember my "bear class"  so i jumped up and down and screamed and yelled and waved my coffee cup. The bear looked at me and wandered off.  My wife got a photo from inside the RV.  I have seen bears run and they are FAST.   Unless you have the gun loose in your hand A fast moving bear coming from cover will be on you before you can pull in out.  In Kruger in South Africa all work crews are guarded by a ranger with a .404 bolt action rifle. Very sad .