Bear Creek Arsenal BC15 12.7x42 Right 18in Right Upper Receiver Heavy Mid-Length 1-20 5/16x24 Flash Hide Parkerized Tungsten. BCA AR15 bolt carrier group and a side charging (Gen 2) handle (patent pending). This 12.7x42 is compatible with any mil-spec AR-15 lower. This has the new handguard. Specifications for Bear Creek Arsenal BC-15 12.7x42 18in Right Side Charging Upper Receiver: Manufacturer: Bear Creek Arsenal Caliber: 12.7x42mm Barrel Length: 18 in Barrel Profile: Heavy Gas System Length: Mid Length Barrel Twist Rate: 1-20 Threads per Inch: 5/16x24 Muzzle Device: Flash Hider Finish: Parkerized 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 Right Side Charging Upper Receiver What firearm models does the manufacturer say Bear Creek Arsenal BC-15 12.7x42 18in Right Side Charging Upper Receiver is compatible with? The manufacturer says that Bear Creek Arsenal BC-15 12.7x42 18in Right Side Charging Upper Receiver is compatible with AR-15Bear Creek Arsenal UASCC5032127X42MHB1812015TNGSR: BC15 12.7x42 Right 18in Right Upper Receiver Heavy Mid-Length 1-20 5/16x24 Flash Hide Parkerized Tungsten