Eastern Arms Company was a trade name used by Sears Roebuck. The guns were manufactured by Meriden Arms, Iver Johnson, Stevens, Savage, and probably others.
Blue Book of Gun Values
Possible places to look include the internet, the library, company website.
UMC refers to Union Metallic Cartridge company. They are owned by Remington and only make ammunition not firearms.
Marlin Firearms: A History of the Guns and the Company That Made Them by William S. Brophy
You can find information about an American Gun Company Knickerbocker shotgun through online firearm forums, gun enthusiast websites, and auction sites that specialize in vintage firearms. Additionally, resources such as the Blue Book of Gun Values or historical firearms reference books may provide detailed information. Local libraries or museums with firearms collections may also have relevant information. For specific inquiries, reaching out to collectors or gun appraisal experts can be helpful.
National Firearms Company was a trade name used by Hopkins & Allen @ 1900.
Not much information is available on Meriden Firearms, but you might go to the library and locate Flayderman's Guide to Antique American Firearms. Then look through all the books on that shelf. The Meriden company was set up by Sears Roebuck to manufacture firearms for sale through their catalog and retail stores. It lasted from about 1905 to 1915.
Firearms marked Hartford were manufactured by Crescent Firearms for the Simmons Hardware Company of St Louis c. 1890-1930.
Check out gunshop.com,they got Lots of info on dbl barrel shotguns.
I can't find a cross-reference for that number, but Eastern Arms was a trade name used by Sears Roebuck. Most of the shotguns were made by Stevens/Savage.
There was no company with that name. Crescent, Davenport, Stevens, and Pieper (Belgium) all furnished firearms for Shapleigh Hardware with variations of the Central Arms name.
Eastern Arms was a Sears Roebuck brand name in the early 20th century. Possible manufacturers include Andrew Fyrberg, Meriden Firearms, J. Stevens, and Iver Johnson.