You are discussing a semi-auto rifle for defensive purposes. You can't let that be the end of the conversation. When you are considering a firearm's properties, and how it will apply to your specific needs, think of you needs in "rings".
The first ring is 'immediate'. That means anything you have might work: .22, .32, .380, 9mm, etc. (a .25, as Jeff Cooper states, may only antagonize your opponent and make him emotional...). This ring is to about the standard 7 yards. (I can't help but put a plug in for a compact .45...).
The next ring is out to about 25 yards. Maybe a nine, but again, .45 rules.
Next is 25-100 yards. Here, shotguns rule.
Then comes the 100-200 yard range. This is the forte of the average battle rifle, and deer rifle. Your 7.62x39 is about the equivalent of your Winchester .30-30. Keep that in mind, you SKS and AK owners! (for thread fidelity, also the Mini-s).
Beyond 200 yards, you can inflict lethal wounds on your deer-sized opponents, but usually only by chance. Here you need a thirty caliber rifle. A bolt action .30 cal will suit nicely unless you are facing the Jihad-hoarde. FN-FALs do well for hoarde suppression, as do M1s.
The bottom line, and my recommendation for an arsenal is: .45 ACP for close, 12 ga. for intermediate, .30 cal for long (semi- or bolt).
The trick is to determine what your specific needs are based on your anticipated situation.
Flame on!
Kit.
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.