Between growing up outside Yellowstone National Park and living in Alaska, I have managed to stay alive with only a browning buckmark on my hip 99% of the time. By far the best item for bear defense is the melon on top of your shoulders. If you really want to be worried about any bear, you...
Here is a website that I have found....many calibers to choose from. Just make sure you enter a bullet weight.
http://www.handloads.com/misc/stoppingpower.asp?Caliber=8&Weight=All