Big difference between a bear or moose and Columbine or Aurora, and any firearm capable of reliably stopping them would be so heavy and big that a backpacker would be unlikely to keep it on his belt 24/7.
Ruger Alaskan .454 Casull seems popular in Alaska, or a Ruger Redhawk in .44 magnum might be what you want.
No handgun will match the stopping power of your shotgun.
But since backpacking requires compromises, and since you mentioned situations where the threats were armed and two-legged, I'll suggest a Glock 20 or 29.
Personally, I prefer a G26 or Pf9 for backpacking, but I have mad skilz to deal with moose and squirrel.
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Last edited by ChuteTheMall; 02-21-2013 at 11:56..