Stone Glacier, Kifaru, and the pack I use now, Paradox, all offer likely candidates for a hunting backpack that can be compact enough for shorter trips, while being able to expand in volume and carry the weight as comfortably as possible in the event of meat hitting the ground... Another newer company that I personally have no experience with, but have been getting good reviews are EXO packs.
Personally, I've been extremely happy with the Paradox Evolution. It's unbelievably light and carries much better than any pack I've owned or used. Including multiple Arcteryx and MR packs. I still have a MR Bighorn, which I like a lot for short trips and day hikes, but if I'm honest the Paradox has kinda made it obsolete... for my uses anyways. The Paradox frame is a modernized external that is extremely stiff where it's needed, but flexes in the right spots too. The pack material is waterproof laminate, which is a nicer feature than I thought before owning it... Did I mention that the pack is LIGHT?!

I'd buy another...
I was a huge fan, but MR has been pretty disappointing to me lately. They build heavy, durable packs and the quality is second to none. Better build quality than most, way better. But again, they've killed off most of the hunting packs I liked and now only offer bigger packs based on the NICE frame... That frame has some major shortcomings and should be phased out. Instead they discontinue the good internals they used to offer and concentrate only on the NICE... Plus we Canucks can no longer buy direct from them... Too bad.
Good luck in your search Phil!