The Geissele Super Duty Build kit features the quality and workmanship you've come to expect from the Geissele name. The complete upper, chambered in 5.56mm, features a Nanoweapon-coated Surefire Closed-Tine Flash Hider mounted to an in-house durable black oxide coated, Cold Hammer Forged, Chrome Lined, 1-7 twist Geissele barrel. Geissele barrels are precision machined, utilizing the highest quality materials at their state of the art facility in North Wales, PA. The Geissele Length gas system and Geissele Super Compact Gas Block (with bomb-proof installation) ensures reliability and optimal performance in extreme conditions and heavy use. The included MK16 Super Modular rail Mfg: Geissele Automatics