The MPX is SIG's closed-bolt gas-operated 9mm pistol-format PCB (pistol-caliber bluderbuster) designed to compete with the HK MP5 and UMP platforms. Unlike many PCBs that use straight blowback operation, the MPX uses a short-stroke piston gas system for improved reliability and a lighter bolt carrier. The pistol configuration with a brace became immensely popular for home defense and competition use. Type: Semi-Auto Pistol Action: Gas-Operated Caliber: 9mm Capacity: 30 Year introduced: 2015, USA Weight: 5.5 oz Overall length: 16" Status: Active Intended use: home_defense, competition, law_enforcement, tactical