I think a pistol caliber carbine makes a lot of sense for urban/indoor CCB, especially if your goal is escape/evasion/disengage. In these situations, you wont likely need a ton of penetration or 200YD+ ballistics.
Several years ago when I was one of the SWAT and Training guys for my dept., we had the opportunity to do some "unscientific" ballistics testing with our duty rounds in various calibers in some apartments that were being demo'd (also got to watch the Bomb guys blow some stuff up for a "Post Blast Analysis" class). We stood at the front door and fired through the walls to test for penetration.
Excuse the crude drawing (and as a Traffic guy, I can't believe I forgot to add "Not to Scale" )...
Rounds fired were:
.45 ACP - 230gr. Hydrashok
.40S&W - 180gr. Hydrashok
9mm - 147gr. Hydrashok
.223 Rem. - 55 gr. Federal HP
Firearms used:
.45ACP - H&K USP
.40S&W - Glock 22
9mm - Beretta 92FS and H&K MP5
.223 - Colt M16A2
The .45 ACP and the 9mm fired from the MP5 penetrated walls #1 and #2 and embedded themselves in #3 to where we couldn't retrieve them.
The .40S&W and 9mm fired from the Beretta penetrated walls #1 and #2 and were barely lodged in wall #3 and were retrieved.
The .223 fired from the M16A2 penetrated wall #1 and fragments were retrieved from the near side of the drywall on wall #2, with a few fragments making their way to the drywall on the far side of wall #2.
It was an eye-opener for us (and more-so for our admin) because at the time we were carrying MP5's for entry due to having a Chief that was a Vietnam combat veteran who told us that an AR would shoot through the house we were entering...and the next two houses down the street.
Having said all that...my bedroom closet gun is a Ruger PCC.