Re: Hunting Pack
These are quite popular and carry a load well and from what you ask for a framer will fit your need. A day pack will strap on the frame and over meat.
http://www.sportsmanswarehouse.com/sport...72545/cat100861
A little better at toting the weight of a moose 5th.
http://barneyssports.com/backpacks/external-frame/frontier-gear-of-alaska-frieghter-frame.html
For toting a rifle, store bought coat / hat hooks can be found and someone makes a carry cradle. I Wasillabilly a coat hook bent steel to make my own. The hook will bolt to holes in the frame. Needs to be short enough to unhook with ease but enough to tote the pop gun.
A freighter pack with external frame carries weight very good on trails and easy terrain. Gets all the weight on the hips. I carried an external freighter for years. I mostly hunted from canoes in 15 until too many hunters ruined the area. The frame allowed a good platform for portaging and toting meat to the canoe on fairly ruff terrain bogs, dead falls, greasy hills.
On ruff terrain and off trail especially hills and side hilling or mountain hunting, an internal does a better job at carrying weight. Distributes weight on the hips and shoulders / chest. For heavy loads like game, the stays or frame should connect to the waist belt like an external, not float, the waist belt needs to be hard and stiff or the weight will flatten it out, kind of counter intuitive. Fancy sculptured soft waist belts are good for ads and weekend backpackers but for real weight in the backcounty for hard users, they are not.
One of if not the best internal freighter store bought pack;
http://www.alaskamountaineering.com/denali-pro/
The problem with buying a backpack is, it should be fit to your body and very few really know how to fit packs. The pack should fit as close to ideal as possible from the packaging then a good fitter needs to adjust it.
Good luck