The H&K MP5 SD is a rimfire rifle. This HK clone is engineered as a dedicated .22 Long Rifle. It's built with a match grade precision barrel, metal receiver, and retractable stock. It also has a Navy pistol grip as well as HK MP5-style sights. The sound dampener (SD) is actually a compensator. It is attached to conceal the 16.1 inch barrel that extends the full length of the gun and compensator.A blowback system operates the .22 caliber HK MP5 SD. When the magazine empties the bolt remains open. Its front sight is adjustable for elevation and comes with interchangeable posts. The rear sight is adjustable for windage and elevation. The safety switch rotates 90 degrees, as does the 9 mm MP5.