NICKEL BORON LEFT AND RIGHT  BOLT RAILS FOR BUILDING A M249, MK46 OR MK48 INTO A FULL AUTO OR SEMI AUTO. ONE PAIR (2) BOLT RAILS.  THESE ARE THE BEST RAILS AVAILABLE. HIGH QUALITY HEAT TREATED STEEL WITH NICKEL BORON.  THE REAR STOCK MOUNT, EJECTION PORT DOOR AXIS PIN AND EJECTOR AXIS PIN HOLES ALREADY DRILLED IN THE CORRECT POSITIONS. EASIEST RAILS TO INSTALL AND THE BEST QUALITY.  THESE RAILS ARE MULTI CALIBER FOR BUILDING A 5.56 OR A 7.62. G I MILSPEC PARTS DROP RIGHT ONTO THESE RAILS WITH NO MODIFICATIONS, EASY ASSEMBLY. THESE ARE THE RAILS WE USE ON OUR MULTI CALIBER MILITARY GRADE MACHINE GUNS.