A slug does not penetrate unless it's moving. Desiring penetration of a black bear is understandable, but it has to be examined in the context of distance and the associated velocity. It's tempting to think that a slug that penetrates best at short range will also penetrate best at long range, but it's not necessarily the case. Furthermore, the best penetrating slug at short range may still utterly if it's called upon to penetrate at an unreasonable range.
Penetration at range is going to be affected by things we can measure: starting mass, sectional density, muzzle velocity, and ballistic coefficient and also how much the slug sheds mass and deforms to affect terminal mass and sectional density. We should expect full-bore slugs (Brenneke, Foster) to have lower sectional density and lower ballistic coefficient than saboted slugs, with wad slugs somewhere in-between. If the slugs start out at 1 ounce, the saboted slug will begin with a big advantage in penetration. How much it deforms, expands, or loses weight could affect the result.
While penetration is important on game and bear can be a formidable target, black bears are wimpy. I live in big western black bear country and I have the data from the state's wildlife biologists on nearly a thousand bears. Around here, a 600 pounder would be one of the biggest black bears. The average mass is around two or three hundred pounds. There's a lot of dudes that are bigger than that. People conflate black bears with brown bears, which are the ones that are about triple the mass with the small brown bears coming in at 800 pounds and big ones going up beyond 2500 pounds -- totally different animal. Without massive amounts of fat and muscle to bulk them up, penetrating the little black bear is not much tougher than a big buck. I can't comment on actual results -- I have a 1 in 100 chance of drawing a tag in any given year and have not drawn one yet. I may never draw a tag in my lifetime. If I were to draw a tag, I would use a rifle. If I had to use a shotgun, I would prefer the trajectory and penetration at longer ranges that a saboted slug offers. Where I can see full-bore slugs being useful would be for bear defense at short ranges, but I cannot offer any recommendations for bear defense as I know nothing about it. I would say that it seems impractical to defend yourself from any predator with a gun you're not carrying at the time of the attack. Carrying a shotgun around all the time seems impractical unless you're doing something like guiding for people photographing bears feeding on a salmon run. Otherwise walking around with your hands full of your "bear gun" might get old. And that bear gun that you keep in the jeep, well, when you get back to the jeep, just drive away.
I can tell you that there is no record of a wild black bear ever killing anyone in California, Oregon, Idaho, or Nevada, ever -- going back 170 years. That's impressive considering how much interaction they have with people compared to Mountain Lions which are hardly ever seen and yet kill a few people in these states every decade.
I wouldn't say that black bear should be regarded as safe, but that people may be needlessly intimidated by them. There have been a lot more tourists from California visiting the forest this year than usual and while locals and regular tourists are accustomed to seeing black bears walking around town, some of the newcomers have not been. It was reported in the news that one fellow kept calling 911 every time he saw one until they threatened to arrest him if he didn't stop calling.
I will say that there are a lot more reports of black bear attacks in Canada. I don't know why that is. While there are probably more bears there, I'm skeptical that there is more bear/human interaction so I suspect that the Canadian bears are meaningfully different in temperament and behavior. Canadian black bears are beyond my scope of knowledge.
Last edited by Western_Juniper; 11/16/20.