Heckler & Koch Hk P7m8 P7m13 Piston Complete Assembly Armorer Parts 9mm Rare December 19, 2023 admin This Heckler & Koch HK P7M8 P7M13 Pistol Parts Piston Complete Assembly is a rare find for gun enthusiasts. Made of high-quality steel material, this silver-colored piston is designed for 9mm gauge/caliber guns.