Sig’s M400 SDI rifle utilizes innovation, performance, and attention to detail that defines other Sig rifles. It is a superior system offering advanced features available right out of the box that was once only found on the after-market. The M400 features a direct impingement gas operating system with a rotating locking bolt, an extended charging handle latch, a flat-top upper receiver, and a built-in tensioning device that eliminates accuracy-robbing play between upper and lower receivers. Ambidextrous controls make the Sig M400 series a perfect fit for right- or left-hand shooters. This SDI model has a carbon steel fluted 16″ nitride coated barrel, brown Cherokee metal finish, black 6-position adjustable stock, and a two-stage match trigger.