The SIG Sauer MPX 8-inch SBR (Short Barreled Rifle) requires NFA registration and offers a middle-ground configuration between the pistol and carbine length, popular with registered class III owners. Type: Semi-Auto Rifle Action: Gas-Operated Caliber: 9mm Capacity: 30 Year introduced: 2016, USA Weight: 6.1 oz Overall length: 26.5" Status: Active Intended use: Home Defense, Tactical