The SIG516 10" upper allow operators to upgrade their current AR-15/M16/M4-type rifles from direct gas impingement systems to the SIG SAUER advanced short-stroke pushrod piston system. This advanced operating system reduces carbon fouling, excessive heat and unburned powder in the action, ensuring reliability and function that is unmatched. A standard 5.56mm NATO chrome-lined chamber and bore ensure reliable function in any environment. Barrels feature an A2 flash suppressor and are threaded 1/2 x 28 TPI, allowing the SIG516 to adapt to a number of aftermarket accessories and suppressor mounts. All upper assemblies are shipped with a recoil buffer and action spring. These components must be installed to ensure proper function of the SIG516 upper assembly on your AR-type lower receiver.