If I were pressed to go into "urban" combat...
I would take the M2 Carbine over the current M4 unit. Not only can I shoot it better, but I wouldn't likely be firing at targets more than 200 yards away. (It would be more like 150 yards distant). I would use 110 grain Soft Point ammunition. These, and a good 1911A1 would let me fight rather well.
What about you?
A bit oc clarification is in order
The .30 Carbine is logistically fine (when you have the proper supply lines). pouches on your field belt can hold both carbine and 1911 magazines with consummate aplomb.
If I can't kill them shooting through structural inadequacies, i'll be surprised.