From The Tactical Wire

Sturm, Ruger & Company, Inc. (NYSE: RGR), announces the availability of three, AR-style upper receiver assemblies featuring the innovative two-stage, piston driven performance of the SR-556® family. These rugged and reliable SR-556 piston driven uppers run cleaner, cooler, and are easier to maintain than traditional gas driven systems, offering significantly improved reliability. SR-556 upper assemblies will be available through firearms retailers and ShopRuger.com.