Howdy, it is obvious that most of you have never lived in an area that is loaded with Grizzlies or have had a roaring Grizzly charging through buck
brush at 20 yards to make you his dinner-and skid on his nose at 5ft from your feet, stone dead from the second shot. No single shot for me in this type of situation! Later
If we're going to include all big bears in that discussion, than I would humbly submit that few places have grizzly densities as thick as the polar bear density in the western Hudson Bay region in the late fall. I've carried a single shot 12 ga and a Ruger #1. The 12 ga proved to be unreliable, so I grudgingly dropped it in favor of other options. It was short and light and a joy to carry. It was also the gun I had with me in what I consider to be one of the hairiest bear encounters I've ever had.
The Ruger #1 I dropped because despite it's power (.416 Rigby) I couldn't figure out a way to prevent the safety from moving to the fire position while the rifle was slung. When I lost it in a house fire, I figured if I was going to have to rearm anyway I might as well do it right so I got a pump 12 ga and a Brno 602 in .375 H&H. The Brno was bought with the intention of turning it into a .458 Ultra wildcat, but when a very good .375 Smith barrel fell into my lap, I opted for the .375 Ultra and never looked back.
You'll note that none of my reasons for switching to a repeater had anything to do with the rate of fire, it had everything to do with safety and reliability. Bear defense shooting is mostly a close range gig. The fellow who shoots a bear at 50 yards and claims self defense hasn't given it much of a chance. Bear attacks happen in one of two ways. Either the bear stalks you and closes to within striking distance, or you stumble onto him in heavy cover. If the bear stalks you and you can see him coming, you let him close until he is close enough that you don't have any option but to shoot, but he presents the biggest target possible. If you stumble onto him in heavy cover, or if he stalks you to within striking distance and you are unaware of his presence, you might be lucky to get even one shot off. If the second shot is not a finishing shot, you won't get it off, so if the speed of the second shot is not critical, then the single shot can be an appropriate tool. Now consider that I mostly carry a bolt gun or pump shotgun with the magazine full but the chamber empty. My single shots had a round in the chamber because if the gun was carried loaded, then by definition it had to have one up the pipe. Chances are if I have to shoot quickly, I'd get that shot off quicker with the single shot.