A rifle is a lot of unnecessary weight to carry when you're backpacking. On long trips especially, you want to travel as lightly as possible. When I go on long expeditions, I don't normally carry any firearm whatsoever. If you know what you're doing, and know how bears behave, you will know how to avoid a bear attack. If you are not familiar with bears, or whatever wildlife you plan on dealing with, bring bear spray or a magnum revolver, and be familiar with it.