Bear Creek Arsenal BC-15 6mm ARC 18in Bolt Action Style Upper Receiver Heavy Barrel 1-8 Twist 5/8x24 Flash Hider Parkerized. Magazine not included. Specifications for Bear Creek Arsenal BC-15 6mm ARC 18in Bolt Action Style Upper Receiver: Manufacturer: Bear Creek Arsenal Caliber: 6mm ARC Barrel Length: 18 in Barrel Profile: Heavy Barrel Twist Rate: 1-8 Threads per Inch: 5/8x24 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 Last Chance: Yes Package Contents: Bear Creek Arsenal BC-15 6mm ARC 18in Bolt Action Style Upper Receiver What firearm models does the manufacturer say Bear Creek Arsenal BC-15 6mm ARC 18in Bolt Action Style Upper Receiver is compatible with? The manufacturer says that Bear Creek Arsenal BC-15 6mm ARC 18in Bolt Action Style Upper Receiver is compatible with AR-15Bear Creek Arsenal UABA-369-6MMAMHB1818-15ASR: BC-15 6mm ARC 18in Bolt Action Style Upper Receiver Heavy Barrel 1-8 Twist 5/8x24 Flash Hider Parkerized