Rock River Arms Mid-Length A4 .450 Bushmaster Completed Upper The Rock River Arms Mid-Length A4 .450 Bushmaster Completed Upper is a precision-engineered, ready-to-run upper assembly built for hunters and shooters who demand performance and reliability. Chambered in the hard-hitting .450 Bushmaster cartridge, this upper features a 16-inch 416R stainless steel barrel with a 1:24 twist rate and cryogenic treatment for enhanced accuracy and extended barrel life. The forged A4 upper receiver is finished in a durable black anodize, while the RRA 13-inch Extended Lightweight Free Float Rail with M-LOK compatibility offers a versatile, low-profile platform for accessories. The low-profile mid-length gas block system provides smooth, reliable cycling, and the included RRA Operator Brake with 5/8-32 threading effectively manages recoil. This complete upper ships with a Bolt Carrier Group, Charging Handle Assembly, and a 5-round magazine, making it a true out-of-the-box solution for any compatible AR-15 lower. Product Highlights Hard-Hitting .450 Bushmaster Caliber: Designed for big-game hunting and serious range performance, delivering substantial knock-down power in an AR-platform package. Cryogenically Treated 416R Stainless Steel Barrel: The 16-inch barrel undergoes cryogenic treatment for improved wear resistance, extended service life, and consistent accuracy with a 1:24 twist rate. RRA 13-Inch Lightweight Free Float Rail: The M-LOK compatible extended free float handguard reduces weight while providing ample real estate for bipods, lights, and other accessories. RRA Operator Muzzle Brake: The 5/8-32 threaded RRA Operator Brake effectively reduces felt recoil and muzzle rise for faster follow-up shots. Complete Ready-to-Install Assembly: Includes a Bolt Carrier Group, Charging Handle Assembly, and one 5-round magazine -- drop it on your compatible lower and go. Specs Brand: Rock River Arms Manufacturer Part Number (MPN): 450B0461 UPC: 842834124138 Caliber: .450 Bushmaster Upper Receiver: Forged A4 Barrel Length: 16 in Barrel Material: 416R Stainless Steel Barrel Twist Rate: 1:24 Barrel Treatment: Cryogenically Treated Overall Length: 24 in Gas System: Mid-Length Gas Block: Low Profile, .936 in Journal Diameter Muzzle Device: RRA Operator Brake, 5/8-32 Thread Handguard: RRA 13-Inch Extended Lightweight Free Float Rail Handguard Compatibility: M-LOK Rail: Full Top Picatinny Rail Finish: Black Anodized Weight: 4.47 lb Includes: Bolt Carrier Group, Charging Handle Assembly, One 5-Round Magazine Disclaimer: We strive to provide accurate and up-to-date product descriptions, specifications, and images; however, errors or omissions may occasionally occur. We are not responsible for any inaccuracies or discrepancies in the content provided. If you notice anything incorrect or unclear, please contact us so we can correct it. When in doubt, we recommend verifying details directly with the product&';s manufacturer. ]]>