Probably the coolist rail on the market and a law enforement preferred. This 16" 556 M4 upper assembly has the forward portion of the Rail as a quad rail with the back portion MLOK. I have this unit on my personal build. Best of both worlds, light weight with the added bonus of the tried and true quad rail and the diameter has been enlarged to accept a silencer. Radical Firearms by far exceeds the rest. If you are looking for top shelf you better get them while they last. Limited quantities of each.   Lifetime warranty No BCG or Charging Handle but but I have some set aside to go with these for $135 extra. Please contact me.  REDACTED