If the "R" stamp is a prefix, the date of shipment is very easy to determine; ship date is 1929, and the gun was manufactured using the standard regular sized ("R") frame. If the "R" stamp was a suffix; the gun would have likely shipped prior to 1920, but as yet no one has been able to determine the meaning of the "R" suffix stamp. The grade of your gun should be stamped/engraved atop the barrels.