Who made the western field 12 gauge shot gun model M550ABR and serial number G780900 and what year was it made?

The Western Field 12 gauge shotgun model M550ABR was manufactured by the Mossberg company. This model was produced in the early 1970s, specifically around 1971. The shotgun was sold under the Western Field brand, which was a label used by Montgomery Ward for firearms. The serial number G780900 indicates it is part of that production era.