Where s the serial number on the Mossberg 20gauge model D-B located?

The serial number on the Mossberg 20-gauge Model D-B is typically located on the underside of the receiver, just ahead of the trigger guard. In some cases, it may also be found on the left side of the receiver or on the barrel itself. It's important to check these areas carefully, as the location can vary slightly depending on the specific model and manufacturing year.