M2 Armament Group AR-15 Streamline 16in Upper Receiver Black. 56 NATO Complete Upper Receiver Group. Engineered for professional armorers tactical shooters and high-volume marksmen who demand unyielding duty-grade reliability. Specifications for M2 Armament Group AR-15 Streamline 16in 5.56x45mm NATO Upper Receiver: Manufacturer: M2 Armament Group Caliber: 5.56x45mm NATO Barrel Length: 16 in Barrel Profile: M4 Gas System Length: Carbine Length Color: Black Gun Model: AR-15 Fabric/Material: Aluminum Gun Rail: Picatinny Gun Type: Rifle Gun Make: AR Platform Barrel Material: Steel Bolt Carrier Group Included: No Magazine Included: No Package Contents: M2 Armament Group AR-15 Streamline 16in 5.56x45mm NATO Upper Receiver What firearm models does the manufacturer say M2 Armament Group AR-15 Streamline 16in 5.56x45mm NATO Upper Receiver is compatible with? The manufacturer suggests that M2 Armament Group AR-15 Streamline 16in 5.56x45mm NATO Upper Receiver is compatible with AR-15M2 Armament Group M2-LPK-M16: AR-15 Streamline 16in Upper Receiver Black