DoubleStar Complete Upper Receiver Standard Flattop with M4 Feed Ramps Black. Standard .Forged from 7075-T6 aluminum that has been heat treated and hard coat anodized. Complete receiver comes assembled with T markings forward assist and dust cover. Specifications for DoubleStar Complete Flattop Upper Receiver: Manufacturer: DoubleStar Caliber: 5.56x45mm NATO Finish: Anodized Color: Black Fabric/Material: 7075 T6 Aluminum Gun Rail: Picatinny Gun Model: M4 Condition: New Magazine Included: No Features of DoubleStar Complete Flattop Upper Receiver M4 Feedramps: Yes Complete/Stripped: Complete Package Contents: DoubleStar Complete Flattop Upper Receiver What firearm models does the manufacturer say DoubleStar Complete Flattop Upper Receiver is compatible with? The manufacturer says that DoubleStar Complete Flattop Upper Receiver is compatible with M4DoubleStar AR220M: Complete Upper Receiver Standard Flattop with M4 Feed Ramps Black