The SIG-Sauer MPX is a submachine gun produced by SIG-Sauer. First announced in 2013, the weapon is available in several selective fire configurations for military and police use. The SIG MPX is a modular weapon which can be user-configured to fire three calibers: 9x19 mm Luger/Parabellum, .357 SIG or, .40 S&W. It is gas operated, utilizing short-stroke gas piston and rotary bolt locking, firing from a closed bolt for enhanced accuracy and safety. It takes ammunition from proprietary box magazines, made of translucent polymer and holding 10, 20 or 30 rounds. Its layout is partially based on the AR-15 platform.