CMMG Dissent Mk4 5.56mm 16.1in Upper Group 1-7 Twist 1/2 X 28 TPI .750in 25.5in Armor Black 55BC737-AB. The 5.56mm DISSENT upper group with a 16.1" barrel is a hard choice to pass up. Pair with a mil-spec compatible lower receiver and the included...