The SIG Sauer MPX is an advantage of a pistol caliber carbine. It’s a gas operated weapon that fires the 9mm round, and features a closed, rotating bolt. These features are designed to make the gun more safe and more reliable to shoot. It also utilizes a short stroke push rod gas system to reduce the recoil of the firearm as well. The advantage here over an AR-15 or any other rifle caliber carbine is the fact that the MPX will be much more compact, nimble, and be easier to shoot in a home defensive situation.