Oh it is chrome lined?? Not Wilson Combat or Noveske then, good chance at an older CMMG, though Im not sure I have ever seen twisted fluting from them.
Could also be a LMT or Barrett, with custom fluting.
If it has 1/2" threads on the muzzle device it would be a Stag with some custom fluting.
No problem on the document, 68forums is a wonderful place for stuff like that!