Probably early part of the century.
If it is a double, remove barrel and you will see it along with serial #.
Made in Belgium.
remove barrel and serial # will be stamped on top of receiver on left
nitro hunter shotgun single barrel with exposed hammer stamped belknap hdwre and mfg serial 5516
1924 - it will be date code stamped on the barrel.
Forget the serial, check the date code stamped on the barrel. See related links.
Don't have 121 serial list, check date code stamped on barrel. See related links.
The primary serial # is stamped on the barrel of the gun opposite the cartrige ejection port
Forget the serial, check the date code stamped on the barrel. See related links.
There should be a stamped model number on the left side of your barrel. The serial number will be on the reciever; however, the model number is on the barrel.
9700.00