Burnsome:  If you will do a little research, you will immediately discover that overpenetration will almost always occur with pistol caliber carbines and subguns.  Contrary to what a lot of people think, the 5.56 rarely overpenetrates.  Look at what the FBI and Dr. Fackler with the US Army Wound Ballistic Laboratory has published.  Pistol bullets are designed to retain mass for penetration, to meet the FBI's criteria for LE rounds.  Most 5.56 rounds tend to yaw and then fragment dramatically on impact with soft tissue or bone.  You want to see overpenetration, then look at what a JHP pistol bullet does when it hits the interior sheetrock wall of a residence.  You will likely see MP5's and Colt 635 SMG's go by the wayside in the next 5-10 years.  A Colt M4 or to a lesser extent the Colt Commando is a much better choice for Close Quarter Battle in an urban environment.  I am personally aware of a lot of agencies who have mothballed their MP5's due to recent studies regarding penetration issues.  Just my $.02.  I would highly suggest you pursue this issue with careful research.  The Hornady Law Enforcement division should be able to supply you with some information.

Our .223's are loaded with Federal 55gr JHP's.
Our 9mm carbines are loaded with Winchester Ranger SXT 147gr JHP's.
Shotguns are loaded with #4 buck.
.38's with 158 gr LSWHP.