This CMMG AR-15 Dissent Mk4 Upper Receiver Assembly is designed to pair with any standard AR15 pattern lower group. Utilizing a patent pending direct impingement Compact Action, DISSENT upper groups house the entire action and recoil assembly in the upper receiver resulting in less bulk and length than traditional AR pistols. The forward non-reciprocating side charger allows for quick bolt operation without coming off target. Direct impingement DISSENTS come equipped with a left side charger standard.