Hello and welcome. From looking at the pics I'm thinking that your shotgun may be a variation of the Mossberg model 183 or 185, perhaps in .410 bore size. They were sold by Mossberg and through several other outlets like Sears and Wards.
The manufacture and model information should be stamped on the barrel, usually on the top or left side in front of the ejection port.
One of the experts here, not me , will likely be along shortly and be able to give you more and better info.
Ride Safe. Dr.Tramp..........