I'm probably of no help to you, Phat; all my backpacking hunting is of upland game with a shotgun. My biggest issue is with ammo. On a three-day trip I carry at least 40 shells -- that's almost four pounds of ammo, even when I shoot my 16. And my Ithaca Model 37, one of the lightest shotguns around, still weighs in at a tad over six pounds. My fifteen pound base immediately becomes 25 pounds.

Perhaps you could rig some sort of travois to drag the animal out?
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My blog on politics, the environment and the outdoors: Haiwee.blogspot.com