One of the most tested and proven weapons systems in the world achieves ultimate refinement with the introduction of the SIG516 rifle. With its Nitride-treated, military-grade barrel and adjustable, four-position gas regulator, the SIG516 incorporates all of the most desirable mechanical improvements. Add to these a free-floating forend, and you have the most advanced, versatile AR-based rifle available. M1913 Picatinny flat top upper receiver and KeyMod handguard accessory-attachment system. A2 flash suppressor. Ambidextrous charging handle and controls. Flip-up iron sights. B5 Systems Bravo SOPMOD 6-position MIL-Spec stock.