Your serial number prefix letters of RN indicate that your Browning 16 gauge shotgun was made in the year 1979.This would indicate that your shotgun was made by Miroku of Japan.All browning shotguns made after 1976 were made by this firm for Browning.All 16 gauge Browning shotguns chambered in 16 gauge were made before 1977.It sounds to me that you could have a shotgun made by Miroku of japan,and possibly have a Earlier Made barrel installed on your shotgun.A standard weight auto-5 shotgun will bring between 325-375 dollars in the condition that you describe,and deduct 30% for the poly choke barrel.