That would be a perfect match for any one of my purple Knights Armament rails.
ETA: My battle buddy recently got a bolt on a new 6920 that can accept a cam pin on either side, and a BCG on a new 6720 that was extremely rough. I'm a Colt guy through and through, and neither of us are too picky about cosmetics, but Colt stuff doesn't seem to be all that perfect lately.
Albert at Colt took care of the bolt in no time flat. Will be interested to hear what response you get. I wouldn't be bothered too much by it, but wouldn't blame you if you are.