Description
The CMMG Mk4 AR-15 Upper Receiver Assembly is a complete, ready-to-install upper built around CMMG’s signature enlarged-ejection-port design and chambered in 5.56 NATO (also compatible with .223 Remington). The receiver is precision machined from 6061-T6 billet aircraft-grade aluminum and finished in CMMG’s Armor Black coating, giving it the same look and finish as the company’s complete Mk4 rifles.
At the heart of this assembly is a 14.5″ steel barrel with a 1:7″ twist. The Mk4’s enlarged ejection port is engineered to clear a variety of alternate bolt-and-barrel conversions in 9mm, 10mm, .40 S&W, and .45 ACP, allowing this upper to serve as the foundation of a multi-caliber AR build.
This upper ships ready to drop onto any mil-spec AR-15 or Mk4 lower receiver and comes with CMMG’s ZEROED polymer dust cover pre-installed.
