hi ploetner,
A two or three letter code on the left side of the barrel identifies the month and year of manufacture. The first letter identifes the month, the other letter(s) identify the year. if you can indentify these it would help. i've got a browning 20 that i turned into a replica of a model 11 trenchgun from ww1 that my wife keeps for home defense. great design.
Kim