Windham Weaponry's Upper Receiver Assemblies are designed as replacement or upgrade units for the AR15 Type Rifle. As with our complete rifles, they are manufactured to the highest standards from the best materials available. Barrels are Chrome Lined for long wear and easy cleaning - machined from 4150 Chrome Moly Vanadium Steel, finished in Black Manganese Phosphate, and rifled 1 Turn in 9" - Right Hand Twist for optimum accuracy with a wide range of bullet weights. Upper Receivers are CNC machined from forged 7075 T6 Aircraft Aluminum and finished in Hardcoat Black Anodize. Bolts are machined from Carpenter 158 Steel - Magnetic Particle and High Pressure Tested.