A 30 round mag of .223 puts out a hail of lead comparable to a shotgun at shotgun ranges, and keeps right on hitting out past 200 yards.
400 rounds of 223 weighs less than 200 rounds of .308, not counting even the extra weight of the .308 battle rifle.
Since we will not be carrying 4 or 5 guns and ammo types on us when TSHTF, I'd just take the .223.
That's a fact. I was writing from the perspective of my own circumstances, which is a suburban neighborhood. Pistol and shotgun territory. On the outskirts, a .30 cal for range.
Your .223 is a good, all-around caliber for defense at 300 yards or less, but not suited to my situation. (don't get me wrong, I love the M-16, but for the average Joe, it is a very specialized weapon for use under not-general conditions...
Kit.