I like pistol cal carbines. I think that they could fill a niche as a survival gun for a few reasons. Obvious one being the pistol/rifle on one ammo diet, that's huge. While 9mm or 45 are both not even close to the effectiveness of a true center fire rifle, at aproporiate distances they are effective. Another big advantage is that pistol ammo is often cheaper that rifle ammo, making it a good choise for stocking up on. If you have a carbine that takes Uzi or Sten type magazines, you can put two of them into each pouch of a mag bag that's designed for AR or AK type magazines. That translates into the ability to have a butt ton of ammo on hand if you want to. I know that the 22 is the winner on that count over all, and that a plan that involves using up lots of ammo isn't sustainable; but it's an option so I mention it.
A big factor that weighs in favor of pistol cartridge carbines is the ability to use suppressors. If you live in a place that allows them, and you get one before the mythical Day of the Brown Fan, you may well still have it in the event that the fan should get browned. Pistol calibers by and large work better with silencers than rifle rounds. You can get subsonic velocity 9mm and 40 or 45 ammo off the shelf. 223 or 308 can be suppressed, but to be "Hollywood quiet" you need a round that moves slower than sound to avoid sonic crack. Again, 22 is the king of silencer rounds, but a 9mm 147 grain hollow point just hits so much harder. Pistol rounds have the best combination of power and suppressability. The ability to pop off a few shots and not have too many people know where it's coming from could be the difference between making a getaway and being overwhelmed by superior numbers. Shoot and scoot, what the angry mobs don't hear won't draw them to you.
