Geissele 5.56mm Super Duty MOD 1 Upper Reciever 16 in Black. Foundational to the renowned quality and performance of this Super Duty system is the in-house produced Cold Hammer Forged chrome-lined Heavy barrel and Nanoweapon-coated Reliability Enhanced Bolt Carrier Group. Both the Geissele CHF barrel and Forged Stressproof Bolt are High-Pressure Tested (HPT) and Magnetic Particle Inspected (MPI) and work in concert to achieve unmatched dependability with match-grade accuracy. The Super Duty features a precisely balanced gas system including the bomb-proofed Super Gas Block and fine-tuned gas port sizing especially when combined with the Geissele Super 42 braided buffer spring (sold separately). These purposefully selected components minimize felt recoil while maintaining reliable cycling even in adverse conditions. The MOD1 features the signature Nanocoated HUXWRX Flash Hider-QD muzzle device offering seamless compatibility with the innovative HUXWRX FLOW series. Rounding out the MOD1 complete upper receiver group the well-vetted center-tab mated MK16 rail features stainless steel QD inserts to reinforce sling attachment. The Airborne Charging Handle provides ambidextrous use and accessibility while maintaining a lower profile to eliminate snagging on gear. Manufactured with confidence and without compromise the Super Duty MOD1 HBAR adds value to the platform while continuing the reputation for excellence. Specifications for Geissele Super Duty MOD1 5.56mm 14.5 inch Upper Reciever: Manufacturer: Geissele Caliber: 5.56mm Barrel Twist Rate: 1-7 Package Contents: Geissele 5.56 Super Duty MOD 1 Upper Reciever .750 Geissele 08-617B: 5.56mm Super Duty MOD 1 Upper Reciever 16 in Black