CMMG's Upper Receiver Assembly is made from forged 7075 T6 AL, and ships with dust cover and forward assist assembly installed. The Mk4 platform accepts standard AR15-style magazines, and is the most versatile of the CMMG platforms, especially with the .22 LR, 5.7x28mm (Conversion), and 9mm conversions. NOTE: Requires charging handle, barrel, handguard, gas block, muzzle device, gas tube and BCG (Bolt Carrier Group) to complete.