It used to be, (not that long ago), if a firearms company wanted to be successful they had to introduce an AR-15 model. Now they are required to have a piston model to achieve that same success ratio. More and more shooters are discovering the upside to going piston as opposed to D.I. My 2 LWRC rifles made me a firm believer of the piston concept. The weapons are all but effortless to keep clean, and run like a Swiss watch. Ruger was smart to jump right in with a piston model, and forget D.I. altogether. The Sig 556 series is also enjoying good sales. A lot do doubt, from it's piston operating system. I think traditional D.I. guns will remain for some time, but in years to come they will go the way of the carburetor in the automotive world. Especially if the military adopts the concept. Bill T.