When modularity, reliability and quality in a 22 Long Rifle package are all important, the Mk4 PDW is the upper of choice. The compact 9" upper offers a great way to have fun at the range without spending extra money in ammunition. The Mk4 PDW is CMMG’s smallest, most compact rifle equipped with the RKM7 KeyMod free floating hand guard and a nitrided 4140 CrMo steel barrel. The Mk4 PDW is available in 300 BLK, 9mm Luger and 22LR.
An “AR-15 Pistol” upper assembly has a barrel less than 16” in length. Pistol uppers are only for use on AR-15 pistol lowers and legal Short-Barreled Rifles. Other configurations may violate Federal law.
Installation of AR-15 upper assemblies with certain features including, but not limited to: flash hiders, bayonet lugs, and threaded muzzles may violate state and/or local laws.