Bear Creek Arsenal BC-15 5.56 NATO 16in Upper Receiver M4 Mid-Length 1-7 1/2x28 Flash Hider Black Nitride. 56 Nato upper is compatible with any mil-spec AR-15 lower. Magazine not included. Specifications for Bear Creek Arsenal BC-15 5.56 NATO 16in Upper Receiver: Manufacturer: Bear Creek Arsenal Caliber: 5.56x45mm NATO Barrel Length: 16 in Barrel Profile: M4 Threads per Inch: 1/2x28 Muzzle Device: Flash Hider Gun Model: AR-15 Handguard Length: 15 in Gun Rail: M-LOK Gun Make: AR Platform Weight: 5 lb Flutes: No Package Contents: Bear Creek Arsenal BC-15 5.56 NATO 16in Upper Receiver What firearm models does the manufacturer say Bear Creek Arsenal BC-15 5.56 NATO 16in Upper Receiver is compatible with? The manufacturer says that Bear Creek Arsenal BC-15 5.56 NATO 16in Upper Receiver is compatible with AR-15Bear Creek Arsenal UAFC4000556MM41617M15TNGSR: BC-15 5.56 NATO 16in Upper Receiver M4 Mid-Length 1-7 1/2x28 Flash Hider Black Nitride