FightLite DFX AR-15/M16/M4 .223 Remington/5.56x45mm NATO 12.5in Upper Receiver Heavy Short-Stroke Gas Piston 1-7 Twist 1/2x28 Manganese. In addition to feeding from M27 linked ammunition the innovative DFX retains the ability to seamlessly transition to standard box type AR15/M16 magazines at user discretion hence its patented Dual-Feed capability. Specifications for FightLite DFX AR-15/M16/M4 .223 Remington/5.56x45mm NATO 12.5in Upper Receiver: Manufacturer: FightLite Caliber: 5.56x45mm NATO .223 Remington Overall Length: 26 in Barrel Length: 12.5 in Barrel Profile: Heavy Barrel Twist Rate: 1-7 Threads per Inch: 1/2x28 Finish: Type III Class 2 Hard-Coat Anodized Color: Black Fabric/Material: 7075-T6 Aluminum Gun Make: AR Platform Colt Gun Model: M16 M4 AR-15 Features of FightLite DFX Drop-On Upper Receiver Group 223 Remington/556NATO 1: Gas-Piston Operation Package Contents: FightLite DFX Drop-On Upper Receiver Group 223 Remington/556NATO