The SR-556 Upper Receiver comes from the factory with a plethora of parts that are popular aftermarket add-ons to the traditional AR platform. These uppers feature an adjustable two stage gas piston system that significantly reduces the amount of fouling introduced to the receiver. The piston and gas tube are both hard chromed to ensure long life and reliability. In fact chrome seems to be a common thread with the SR-556 upper. The bolt carrier, gas regulator, and barrel (hammer forged in-house from Mil-Spec 41V45) are all chromed. The barrel is available threaded or with permanent flash hider. Also featuring folding detachable iron sights, and quad rail forearm.