‘C’ is found on both Damascus and fluid steel barrels and is presumed to represent Crucible Steel Co. of America established in 1901.
‘S.B.&Co C’ - Sanderson Brothers & Co. Cumberland (Maryland) Works? or Carpenter Steel Company, establish in 1889 in Reading, PA which used a ‘C’ to mark their bar steel?
Without internal Hunter Arms documents I don't think we'll ever know, but the search is part of the fun