Serail number and features
About 1973
IIRC, Cornell Publications might have a book that can help
Please list all the markings on the shotgun. Harrington & Richardson were producing hammerLESS double shotguns as far back as 1882. sales@countrygunsmith.net
No such maker. However, if it is Harrington and Richardson, you will need to see if Cornell Publications still sells a book with H&R sn information.
serial number suggests a single barrel, hinged frame Model 1908/08 shotgun - if so - 1920-25.
That should be 1975
"AD" prefix indicates 1967
what letter or letters are in front of serial number
The prefix letter shows the year of manufacture. 1956 is letter S
"AX" prefix indicates 1981
The manufacture date of western field model M782 with the serial 830424 is 2012.