SIG Sauer MPX K 9mm Pistol, 4.5-inch Barrel, Short-Stroke Gas Piston, 3x 30-Round Magazines. This SIG Sauer MPX K brings the compact 4.5-inch barrel configuration together with the MPX's short-stroke gas piston system and rotating-bolt lockup. It features a dual-rod telescoping brace, flip-up rear sight, and short Picatinny rail sections at 9 and 3 o'clock. Also comes with a pelican case with some extras.