The web site below says between 1950 and 1955. I just bought one. http://home.epix.net/~damguy/mossberg_shotgun_models.htm
This is correct as I bought a brand new one in 1952 when I was 12 which I still have.
Your western auto model 312AA shotgun was made by mossberg for western auto.The mossberg model 395,395K are the mossberg model designations for your shotgun.
Mossberg made them Mossberg Model 500 is the same!
Mossberg
Mossberg made that shotgun for Montgomery Ward's Western Field fun line. It was the Model 185 in Mossberg shotgun line.
Mossberg
Your shotgun was made by Mossberg for the Montgomery Wards Company(Westernfield).The Mossberg model 500ab is the same shotgun as yours.
The western field model 172B was made for Montgomery Wards(Western Field) by the firm Mossberg and sons.The Mossberg model 395K and your shotgun are one and the same.The Mossberg model 395K was made from 1963-1983.
The Mossberg model 185D bolt action shotgun was made from 1947-1959.
Mossberg and sons is the manufacturer of your western field model M550ABD,shotgun.The Mossberg model 500 is the same shotgun.
mossberg
Probably Mossberg
500.00