Ruger SR-556 5.56mm NATO Two-Stage Piston Autoloading Rifle – RUGER FIREARMS – rugerarmsstore.com

THE AR PLATFORM REDEFINED. The SR-556® offers Rugers legendary rugged reliability, and comes factory standard with a host of accessories that todays shooters demand. Employing a patent-pending, chrome-plated, two-stage piston driven operating system that provides the user with a cleaner, cooler running, reliable firearm that is truly state-of-the-art.