Owlnmole
I like the ballistics of the 30 carbine, but I don't like the price nor the availabity. There was a time when you could find 30 carbine on the shelf, but not anymore.
I'd love a carbine designed for moderate range, an 'urban sprawl rifle' if you will. It would have to have more power than a 45ACP, power equal to or less than a 7.62x39
Also, the ammo would have to be readily available, and relatively inexpensive.
To me, that leaves 2 ammo choices, 357 and 44 mag. Yes, 30 carbine and 45automag and 10mm all fit in there too, and all 3 of those are probably easier to make a semiauto carbine around. Still I cannot easily zip past the local sportinggoods store and expect them to have a few boxes. That also applies to TEOTWAWKI types as well, exotic calibers don't fetch as many scoops of Dog Gumbo.