Bear Creek Arsenal BC-15 .450 Bushmaster 18in Upper Receiver Heavy Mid 1-24 Twist 5/8x32 Flash Hider Parkerized ODG. 450 Bushmaster upper is compatible with any mil-spec AR-15 lower. Magazine not included. Specifications for Bear Creek Arsenal BC-15 .450 Bushmaster 18in Upper Receiver: Manufacturer: Bear Creek Arsenal Caliber: .450 Bushmaster Barrel Length: 18 in Barrel Profile: Heavy Gas System Length: Mid Length Barrel Twist Rate: 1-24 Threads per Inch: 5/8x32 Muzzle Device: Flash Hider Finish: Parkerized Color: OD Green Gun Model: AR-15 Handguard Length: 15 in Gun Rail: M-LOK Gun Make: AR Platform Weight: 4.5 lb Flutes: No Last Chance: Yes Package Contents: Bear Creek Arsenal BC-15 .450 Bushmaster 18in Upper Receiver What firearm models does the manufacturer say Bear Creek Arsenal BC-15 .450 Bushmaster 18in Upper Receiver is compatible with? The manufacturer says that Bear Creek Arsenal BC-15 .450 Bushmaster 18in Upper Receiver is compatible with AR-15Bear Creek Arsenal UAFC4012450MHB1812415ODGSR: BC-15 .450 Bushmaster 18in Upper Receiver Heavy Mid 1-24 Twist 5/8x32 Flash Hider Parkerized ODG