I didnt read all of the replies so if i repeat something that has been said I apologize. the 9mm...or anything that glock chambers do NOT make the list for handgun calibers I would use for bear defense. 44 mag with 300 grain hard cast bullets are cheap to shoot and thump prett hard and you can get it in a wide variety of revolvers so you can go as big or as small as you with. next up is the 454 casull lots of power and pretty good selection of guns. go heavy on bullets. then you get your S&W X frame revolvers which are awesome but heavy. In my experience a heavy gun get packed less than a light one in day to day use (however I dont expect polar bears in rural wyoming) the 460 and 500 both would put about any bear in its place quickly. Personally the mountain lite S&W 44mag would get a LOT of consideration. if weight is a non issue I have had a lot of fun with the 460 S&W keep this in mind. you will likely wish you had more gun but probably never wish you had less gun. especially when something wants to eat you
Anything less than overkill is underachievement!
" Real elk guns start with the number 3 or bigger and blow two holes, one in and one out." - My Dad
This is just my opinion. Glock model 20 sf 10mm with a lone wolf longslide upper 6 inch barrel. Using 200 grain beartooth or double tap flat wide nose hard cast. When you go to a short barrel in a revolver you are losing a ton of velocity and energy. With our 10mm loads we are exceeding 44 mag energy with a 3 inch barrel. Confirmed through chronograph. With a 6 inch 44mag same load we are equaling energy with our 10mm. I'm not saying you can't get a hotter 44 load either. I had lone wolf build this for me last year and love it. I had them open the leads in the chamber to accept these bullets for dependability. Goggle what fish and game uses for polar bear country sidearm in Alaska? no I'm not saying this is the best choice for everybody But this is what I would take. With a plus 2 mag ext. I have 18 rounds with close to 900 lbs energy.
+1 For the Glock! I also chose the Glock model 20 sf 10mm for my brown bear hunts for the above same reason! I have shot a lot of combat pistols and you just can't beat the reliability of the Glock auto in those types of conditions. The revolvers are nice, but low round count.
Just my 2 cents.
Just another thought. When I think of a defensive weapon I think of two main things; familiarity with the weapon and the ability to make the shot. If you are shooting 10,000 rds a year competitively with your glocks its pretty safe to say that both of those aspects should be covered.
Now there isn't much that would stand up to a hit from a big bore revolver, but then again, you have to hit it....and the 10mm with a heavy bullet can pack a punch.
I personally would feel more comfortable and confident with a weapon that I have spent countless hours behind than that of one that I was unfamiliar with. Theres a big difference in form, function and recoil of a magnum revolver compared to the familiar glock.
I run a Ruger super redhawk alskan in 44mag, I'm in Alaska worried more of brownies than polar bears. I've shot several different loads through mine everything from 240 gr sp to the buffalo bore +p+340gr hard cast that are my personal choice for a defensive gun in the bush. I've only staired down moose so far and not been worried about a bigger gun. A heavy 44 load is near the top of most people's pain threshold and ability to make accurate follow up shot(s). 454 although impressive in numbers is not so impressive in the follow up shot capability for me anyways I've shot handguns my entire life. A lot of the wkend warriors here carry 10mm if you are atv riding or snow machining with the chance of filling you gun with mud and crap then a 10mm glock is hard to beat. You will be in a helicopter most of the time so weight shouldn't be much of a concern, nor mud the diamond d holsters are high quality and will probably out last you. I've always been a fan of 44mag and heavyoads even for deer back home, 44 mag Ruger redhawk in a short or even 4" barrel and some real loads will be more than enough to keep you safe. Getting a bullet to penetrate the central nervous system is the key to stopping a charge dead in it's tracks, usually that means a brain shot. I've seen studies of bears being killed by hunters that had 357, and 9mm bullets just under the hide. Shoot one in the face with a lesser caliber may very well stop his forward progress but if I'm shooting one in a defensive situation I want all the help I can get. Get a Ruger super redhawk thwyre make to take the heavy loads unlike some other brands. Do some checking on hsm and buffalo bores websites on which brand is safe to use their heavy loads in and you'll quickly see which gun you'd rather carry.