Battle Arms Development 5.56 Caliber Lightweight Upper Receiver Gen2 Black. 56 Caliber Lightweight Upper Receiver Gen2: Manufacturer: Battle Arms Development Color: Black Finish: Type III Hardcoat Anodized Fabric/Material: 7075 T6 Billet Aluminum Caliber: 5.56x45mm NATO Gun Make: AR Platform Gun Model: AR-15 Condition: New Package Contents: Battle Arms Development 5.56 Caliber Lightweight Upper Receiver Gen2 What firearm models does the manufacturer say Battle Arms Development 5.56 Caliber Lightweight Upper Receiver Gen2 is compatible with? The manufacturer says that Battle Arms Development 5.56 Caliber Lightweight Upper Receiver Gen2 is compatible with AR-15Battle Arms Development BAD556-LW-UR: 5.56 Caliber Lightweight Upper Receiver Gen2 Black