What is the value of a 12 gauge single shot break open shotgun made in the year 1900 and on the month of December on the 11 day?

Answer 1

That is the date a patent covering some feature of the gun was issued, not the date it was manufactured. This date may be found on several shotguns made by J Stevens Arms and Tool Company and its later operations as J Stevens Arms, Stevens/Savage, and Savage, so about all we can say about its age is that it was made sometime between 1900 and 1991. Almost any Stevens single shot made after 1900 is worth between $25 rusted or busted and $100 like new.