The following link should take you to a list of serial numbers relative to dates for Rigby but I’m not sure if the serial numbers for the ‘D’ & ‘C’ grade guns are part of this series.

As regards information on your individual gun I’m afraid the wastes of time that currently own the Rigby name are refusing to release any information from their records (something of a PR & financial miscalculation by them).

http://gunshop.com/dgsnos4.htm

Regards
Webley