I think it depends on what your needs are. For example, if the question is only “what can stop a bear?†then the answer will be “The largest, fastest, heaviest projectile you can sling in its direction.†If the only requirement was “I need something that will stop a bear quickly,†then I would suggest something like a 12g slug, or a .45-70, or maybe a .375 H&H.
However, the question is usually posed as “I need something for bear defense while fishing.†Or “I need something for bear defense while hiking in the woods.†Then the conversation shifts. Then it starts to become a practicality conversation. See, I know for a fact I would be better off packing around a .47-70 lever rifle in bear country… But it just flat isn’t practical. Over the 4th, I did a long back-packing trip into the wilderness here in Montana. Over 3 nights we did roughly 38 miles carrying 70+ pound packs. Throwing a lever rifle on top of that (and making it accessible) isn’t practical. I’m also dealing with more than just bears: Wolves, Mountain Lions, Badgers… The list goes on.
This is the point that opinions start to enter the debate. Anyone familiar with firearms understands that a large, fast projectile is going to have the most energy. But for times when simply having the largest and the fastest isn’t practical you have to start compromising. The question then becomes.. How much do I want to compromise, and where do I want to do the compromising?
For example: you might decide you want to compromise on size only. So, instead of carrying a rifle, you might take a pistol. If that is the only compromise you would take the pistol that shoots the largest, heaviest, fastest bullet available in pistol format… You would likely look at a .500SW, for example. The point being: the second you decide to compromise away from the heaviest and fastest, you are giving up some “bear stopping†ability, but you are meeting additional needs beyond “bear stopping.â€
Personally, and this is where it becomes nearly all opinion and less science. I need something that has enough energy to stop a bear (in my opinion), enough capacity to be used for other threats (in my opinion), and light enough to be carried comfortably (in my opinion), and small enough to be easily deployed in an emergency.
For all of those reasons, I made the decision to carry two things in bear country: good bear spray, and a pistol small enough to be carried on the side of my pack but still have enough power to put down a bear. That’s why I went with a 10mm 15 round 220g hardcast capacity pistol. I give up bullet size for capacity. I give up barrel length (extra FPS) for a more compact and manageable size that weighs less. It is nothing but a series of compromises away from what is “the bestâ€: the largest, heaviest, fastest projectile. What people should ask themselves is very simple: at what point away from “the largest, heaviest, and fastest†am I comfortable using? What is the point that I no longer feel comfortable? If your answer is “at no point,†then you carry the largest, heaviest, and fastest. Everyone else will fall on some kind of spectrum, from X caliber up to the largest, heaviest, and fastest and everywhere in-between. But that really changes the question from “what’s the best†to “what are the compromises you are willing to make?â€
What lead me to my decision was a whole lotta research and some real world experiences. I’ve personally watched a black bear take 7 hot rounds from a .357mag and keep fighting dogs like it just got stung by a bee. I’ve personally watched a black bear take a .44mag to the head and drop like someone turned off the lights. I have yet to use my 10mm as bear defense (Thank God), so I can’t provide you personal real world experience. I do know it’s good enough for the Siriuspatruljen (http://en.wikipedia.org/wiki/Sl%C3%A6depatruljen_Sirius) whom encounter Polar Bears regularly, and it’s good enough for many guides in Alaska (http://forums.outdoorsdirectory.com/showthread.php/109570-Alaska-Guides-carrying-10mm-for-Bear-Defence-Sidearm) , part of the reason it meets MY requirements and MY compromises.
Of course… That’s just MY opinion.
