That is a rifle length buffer tube. It uses a 5.9 inch rifle buffer in an AR15. In a 308AR, the buffer is 5.2 inches. Like @98Z5Vsaid earlier, the rifle length buffer tube cannot use a carbine/collapsible stock. You must have a rifle stock. With your goal of maximum felt recoil reduction, the rifle buffer system with the XH buffer linked earlier will be your best bet.