Quoted:
The 9mm is a handgun round. Putting it in a carbine does not increase the velocity much over a handgun.  So the stopping power is not increased that much over a handgun.  The advantage is shot placement and the ability to put more rounds on target vs. a handgun.   Comparing the 9mm to a .223 or 7.62 round it loses.   Entry teams across the USA dropped MP5's in favor of 5.56 carbines and SBRs.  The 5.56 round has much more stopping power.   The myth of a 9mm round not overpenetrating vs a 5.56 round is just not true. Both will penetrate sheetrock. The question is what round has more lethality after going through sheet rock?  I was under the impression the 5.56 round broke up and was less lethal after going through sheetrock but now I am not sure.