CMMG DISSENT Mk4 5.56x45mm NATO 10.5in Upper Receiver 1-7 Twist .750in 1/2 X 28 TPI Anodized Black 55B8D86-HCA. 5 DISSENT 5.56 is a ton of fun and its rowdy Now that we got that out of our system our ears quit ringing and we arent seeing fireballs...