Bear Creek Arsenal BC-15 12.7x42 18in Bolt Action Style Upper Receiver Heavy 1-20 49/64x20 Flash Hider Parkerized. 7x42 upper is compatible with any mil-spec AR-15 lower. Adding any other product to your cart will not allow you to check out. Magazine not included. Specifications for Bear Creek Arsenal BC-15 12.7x42 18in Bolt Action Style Upper Receiver: Manufacturer: Bear Creek Arsenal Caliber: 12.7x42mm Barrel Length: 18 in Barrel Profile: Heavy Barrel Twist Rate: 1-20 Threads per Inch: 49/64x20 Muzzle Device: Flash Hider Finish: Parkerized Color: Black Gun Model: AR-15 Handguard Length: 15 in Gun Rail: M-LOK Gun Make: AR Platform Weight: 6 lb Flutes: No Package Contents: Bear Creek Arsenal BC-15 12.7x42 18in Bolt Action Style Upper Receiver What firearm models does the manufacturer say Bear Creek Arsenal BC-15 12.7x42 18in Bolt Action Style Upper Receiver is compatible with? The manufacturer says that Bear Creek Arsenal BC-15 12.7x42 18in Bolt Action Style Upper Receiver is compatible with AR-15Bear Creek Arsenal UABA339127X42MHB1812015ASR: BC-15 12.7x42 18in Bolt Action Style Upper Receiver Heavy 1-20 49/64x20 Flash Hider Parkerized