Re: 223 16 in or 20 in barrel
I think of the .223 as a Varmint round, and try to optimize my rifles in that chambering for max velocity/range.
For CQB, a short barrel is better, and I like either the 44MAG or the 20ga.
If I ever need to whack at someone across spitting distances, I'm going to want to whack at them with something that has a bunch more punch than a woodchuck slayer. Personally, I can't handle a lot of 12ga recoil, so I choose something that has shotgun capabilities, with recoil I can take a more repetitions from.
Greg