I've had a number of full size packs and I think I've found: the one.
It's made by Seek Outside. The Revolution Fortress.
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Light - about 4 lbs.
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Waterproof.
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Large - with the added outside pouch that you can use as a daypack, almost 8,000c.i. total.
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Comfortable. Last thing I hauled with it was a brown bear hide and skull this past fall. They are notoriously heavy, but it handled the load well.
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Probably can get a moose quarter in the bag itself, but you could strap it to the outside or take the bag off and strap it to the frame.
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The frame is very small, and it's hard to tell that's it not an internal frame pack.
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An open pouch, low on both sides of the main bag, for water bottles, spotting scope...
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It's light enough and comfortable enough that I use it for everything.
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Um, expensive.
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And like Monterey, I've also still got an old Camp Trails freighter frame. The moose bag is long since worn out, and I had to replace the waist belt. But it's light and cheap and still gets the job done.