This CMMG AR-15 Upper Receiver Assembly is designed to pair with any standard AR15 pattern lower group. Harness the capability of 22 ARC in this uniquely designed 16.1upper. The 22 ARC is the result of careful and meticulous design, following the same proven methodology as the highly acclaimed 6mm ARC. The cartridge and chamber were designed concurrently by Hornady to ensure consistent and repeatable function while producing 22-250 performance from the AR-15 platform. 22 ARC barrels feature an optimal 1:7 twist rate to better stabilize the heaviest 22 caliber bullets.