The Sig Sauer M400 Tread Semi-Auto Rifle operates with a direct impingement gas operating system with rotating locking bolt. The M400 Tread semi-automatic rifle comes with a 6-position Magpul SL-K collapsing stock and a free-floated M-LOK handguard. The rifle operates with a mid-length gas system, a single-stage polished and hard-coat trigger, and ambidextrous controls. The 16″ stainless steel barrel comes equipped with an open-prong flash suppressor. The 7075 aircraft grade aluminum forged lower receiver features an anodized black finish. A receiver Picatinny rail allows you to attach optic sights. The Sig Sauer M400 Tread Semi-Auto Rifle functions with both 5.56 x 45 mm NATO and .223 Rem. ammo, and is compatible with most M16-type magazines.