It does make sense, of course when one is out of ammo they are completely out. I think your friend will be surprised how much “long range” he will need in an urban setting. If I am understanding your post, he wants to use a pistol caliber carbine and a pistol in the same caliber. Look at the ballistic data. 9mm is a common cartridge and has killed a lot of people (WWI, WWII, and every thing sense) so all egos aside look at its performance. From a 16 inch barrel it is easy to use out to 100m. about 115-125m (depending on load/cartridge and carbine) it begins to drop quickly. Depending on your zero (distance from shooter to target) it can really drop fast. I have several of them and am very comfortable with them – inside of 200m! But, I also know my hold over for a shot to hit at 200. Just my thoughts.