These packs are pretty cool, we used to use them in South America. This, or something very similar, are standard issue for the Honduran Ranger battalion. It's great for carrying a shotgun in, or swapping your main rifle out to use the shotgun for close work on setups like labs or bunkers. You can run your AW on a three point and just let go of it to grab the secondary.
Eberlestock Gunslinger Backpack systems
It's easy to modify the scabbard pocket by tearing a seam and re-sewing it so you can just take it out and stick it back without a huge amount of effort, but it still holds the weapon fairly securely. As long as you're not banging the stock off of trees and rocks all the time, it's a really convenient item. There's a couple of these pockets that will just barely take an AK or small Streetsweeper drum. And you can reach into the main cavity from the side, so you can carry flares, mags, pistol, canteen or a full size Streetsweeper drum. Or if you're like some of those Honduran dudes, all of the above plus cheese and wine.
You can also drop in a Camelback bladder, for water when you've got to put some distance on without stopping.
This is going to be my main scramble bag for bugging out when SHTF.
'preciate the link, there. I've been missing mine ever since I got out and the shippers "lost" it, along with my Glock 20, the Javelina and some other nifty stuff...