The Spike's Tactical ST-15 Enhanced upper line-up is designed as a fully Mil-spec compliant upper series for law enforcement. This same level of quality and performance is now available to everyone, all at a price range that is affordable to shooters of any budget. Each component is manufactured to Mil-spec standards. This model features 16" with 1:7 Twist cold hammer forged Mil-spec Barrel, ST Optimum Profile, Mid Length Gas System, ST Micro Gas Block, .750" Diameter Gas Seat, Spike's Tactical Mil-Spec M16 Bolt Carrier Group, ST BAR2 12" Rail, and A2 flash hider.Our complete upper assemblies will arrive to you inspected, tested, and ready to drop-in and go to work. We maintain our high standard of tolerances and attention to detail as the uppers we use for complete rifle builds. Every built upper and complete gun is test fired before leaving our facility for function check before it reaches you. We offer several rail choices and rail lengths. Use the drop bar to make your selection. Feature: M4 feed ramped barrel extension Solid billet steel low profile gas block Black nitride inside and out mid length gas tube Mil-Spec type 3 coating forged aluminum charging handle Phosphate M16 complete BCG