David, I am looking at my 1939 reprint of the Shooters Bible and it looks to me your gun is an Iver Johnson. The shape of the forend matches as do the screws on the side of the receiver. It could be nickle plated for an additional .40. Guages were 12, 16, 20, 28 and 410 per the catalog. I do have to agree with George above. Can you simply look at the gun to see what is written on it somewhere. Almost all American firearms have the manufacturer or a brand name somewhere. I would think opening the gun and dropping a shell down the chamber would be a safe way to ascertain gauge though it is probably stamped on the gun somewhere. The forend should simply pull off the barrel. I hope this helps.
|