Im working on my xm3 rifle and need proper ring height using nightforce ultra lite 30mm rings.Specs that i have for the rifle are,#7 contour barrel,20moa nightforce base, and the scope is the Nsx 3.5-15x50.Those who have this or similar set up please advise on which height ring to go with.Mediums or Lows?.I dont want any clearance between barrel and scope bell.thanks in advance.