Found a reference to the documentation: http://www.calguns.net/calgunforum/s...d.php?t=317669
Specifically: Click image for larger version. 

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and "Again, note that no dimples may be present for any of the three FCG holes."


Just for the record, I'm not defending the ATF's "right to exist", just providing history and just where this may have gone afoul of previous rulings...