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Online! Search Iver Johnson information; There are forums that have experts or links to answer any question you have. I have yet to find a single source for everything Iver Johnson...
I know where there is one. It is in NICE condition. Where are you located?
If you've ID'd it as an Iver Johnson product, I'd guess it is a Champion model which was made from 1909 to 1956. I think Sears may have dropped the Eastern Arms name sometime earlier than that, probably in the 1930's.
Type your answer here... Remove the two screws on the butt and you will find a single screw inside that holds the stock on. Remove the screw and the stock can be removed revealing serial number on top.
Numrich (Gun Parts Copr.) has some Iver Johnson parts.
the 'bluebook'
Newport guns were made by a variety of manufacturers for Hibbard, Spencer, Bartlett & Co. Known makers are Crescent, Davenport, Iver Johnson, and Stevens. Best bet for a 410 single would be Iver Johnson's Champion model.
gunpartscorp.com has the best collection of Iver Johnson parts
Generally, you can't. If you can identify the model, you can determine the years in which it was manufactured, and sometimes narrow that down by variations in the model's specifications.
Garage sale, want ad, pawn shop, on line auction, gun shop, gun show
To determine the age of your Iver Johnson side-by-side 12 gauge shotgun, you'll need to check its serial number against the manufacturer’s records, as they can provide information on the year it was produced. Iver Johnson produced firearms from the late 19th century until the mid-20th century, so the age can vary significantly. If you provide the serial number, you may be able to find more specific details about its manufacturing date.
These were made by Iver Johnson company. Try searching gunpartscorp.com under Iver Johnson,