efficient with a can, GI replacable parts, mags, ammo, can't have a .22 unit, etc. So the AR 223's "needing" a barrel looks REAL small as a problem, compared to the problems ALL 308's have as a decent shtf rifle.
You think in a world where everything occurs in 50m to 75m, the laws of physics and ballistics can be broken as easily as man made laws, there is no ability or need to ever penetrate cover, you'll never need a sleeping bag in winter, everyone is a psycho who will flock to gunfire, and everyone spends their lives hiding behind the bushes all day, with a canned rifle, waiting for the next guy to make his move so he can be popped for the last can of beans.
My sugestion would be to stay in terrain that conforms to your thinking. Pagosa Springs and the surrounding area is not the type of terrain that conforms to your thinking.
BTW, I do agree that for most of the USA, the AR-15, with a barrel of at least 16" is a pretty good SHTF gun, and the .22LR unit is very handy. This is the rig I currently use.
However, the CAR-15 is NOT the end all be all, and that doesn't mean all other weapons are junk - far from it. I also have a tack driving .308 scoped Kar98k Mauser in the bugout inventory.