If you want a gun that can stop a grizzly intent on eating you then forget about every single military style semi auto weapon you have ever seen (SKS, AK, AR, etc...). The cartridges are not designed to stop charging bears. They are designed to be human killers/ wounders and be light enough and small enough so that a soldier can carry lots of ammo.
The 7.62X39 isn't regarded as a good deer cartridge much less a grizzly stopper.
Forget about getting a semi auto rifle all together. The last thing you want is to get a jam when the bear is trying to eat you. Semi autos have a knack for not working in extreme cold weather and most semi autos can not handle a cartridge big enough to count on to stop a Grizzly quickly. There are a few exceptions but you are going to spend
$$$$$$$ for one.
I would also forget about a single shot rifle. One shot is about all you would have time for before the bear got to you. Reloading is very slow in a stressful situation such as this. You have to break open the gun, fumble getting a cartridge in your hand and get it into the chamber and close the gun all the while trying to stay alive.
If the firearm isn't chambered in a .338 Winchester mag or larger then I wouldn't even consider carrying it to be used as a grizzly stopper. If 1000+ pound bear is charging me then I want to throw out the largest chunks of lead as fast as I accurately can.
Your best bet is a pump shotgun. They are simple to operate and operate fast, they throw huge chunks of lead or multiple smaller chunks of lead, they are as reliable as a gun gets and are very rugged, and they don't cost much.
Winchester makes a model 1300 defender that has an 8 shot magazine tube and a 18" cylinder bore (no choke) barrel and synthetic stocks. It should retail for under $300 US new. This would be my choice as it has a rotating bolt head that locks into the barrel (stronger design), holds two more shells, and unloaded is a full pound lighter than the Remington.
Remington also makes a shotgun that is very similar to the 1300 except that it only holds six shells in the magazine tube. It too has an 18" cylinder bore barrel and synthetic stocks. It's the bottom one in the pic.
