If it was manufactured prior to 1968 it probably doesn't have one.
If you cannot easily see a serial number, then it was manufactured prior to 1968 and doesn't have one.
Serial numbers were not required before 1968
There may not be a serial number on the gun. If that gun was made before 1968, .22s & shotguns often did not have serial numbers. In 1968, a law then required all firearms to have a unique serial number.
On what?? Many firearms before 1968 did not have serial #'s.
IF it has a serial number (not required in the US until 1968) it will be stamped on the receiver.
If there is no serial number, it is a 1960's model-up to 1968. In 1968 a law was passed requiring all guns to have a serial number.
If your Colt Stagecoach was made from 1965 - 1968 it will not have a serial number.
No serial number as the Hunter was made up to 1964 and serial numbers began in 1968
1968 2,030,404 Above was first serial number for 1968. Following year began with 2,172,356.
1968
If you have a common shotgun made before 1968, there probably is no serial number to look up. If the serial number is not on the receiver some where; i.e., water table, side, bottom, somewhere; then it doesn't have one & that is as far as you can take the serial number of a shotgun made before 1968.