No serial number = no way to answer.
serial #
1983
1977
2006
1951
It was made in 1981.
15386
1928
The 2 letters in your serial number dates your shotgun to the year 2004.
No way of knowing without you providing the model number/name of the shotgun and the serial number that goes with it.
It depends on the serial number, one cannot get the date of manufacture with out the serial number