I found this, part of an old post,,,,,
Havlin replied:
590 marine cote made since 1988.
First finishes were high polished and looked like stainless. By 1992, they had dulled it down to a satin finish, still silver, and today the finish is almost a dull matte gray - the users didn't want the glare off the high polish finish so Mossberg adjusted.
None made with stainless, but that first finish looks that way and confuses many
What is your serial number?