I respectfully disagree. A pistol caliber out of a 16″ barrel has considerably more power than the same cartridge from a 4″ or 5″ pistol barrel. 9mm ammo has come a long way and is a potent defensive round, and even more so from a carbine. 9mm is also the least expensive center-fire pistol caliber and available almost everywhere. Certainly less expensive than 5.56 NATO or .223. To many, price is an important consideration, not to mention that in a number of growing areas owning an AR or similar rifle is increasingly difficult.
