Hello,
Your friends revolver was shipped in January of 1865. The finish would have been blue as nickel plating did not become available until around 1870. As far as the spacing between the barrel and cylinder I have no idea what the specification is, however 1mm does seem excessive. I measured a New Model Army and a New Model Navy and both spacings were about 0.127mm.
I hope this helps.
Regards,
Bill