These guns were store-brand guns built by Stevens. Most were not serialized and if yours is there is no serial number chart anyhow. That is probably an assembly number or other in-house number used to batch parts. Value will be under $100. sales@countrygunsmith.net
I got one from e-gunparts.com, which is Numrich. They have schematics for many guns.
nitro hunter shotgun single barrel with exposed hammer stamped belknap hdwre and mfg serial 5516
50 Bucks...
Depends on what is marked on the gun.
I posted a link in the related links section that may be of some help.
The Riverside trade name was used by J. Stevens from 1915-mid 1940's. You MIGHT be able to get a precise date by contacting the Stevens historian. savagearms.com should have his contact information.
This a double barrel shotgun. This is my second favorite shotgun in the world. The reason why it is called 12 Ga double barrel is that the barrel in 12 inches long, and every two shots, it has to be reload.
It's an off-branded Stevens Model 311, worth $150-$250, made between 1920 and 1948.
If it is a double, remove barrel and you will see it along with serial #.
thomas jackson of london england
An older used utility double barrel shotgun is worth around $200 if it is fully functional, but not in like-new condition.
It's date code stamped on the barrel, see related links for information on the Remington Society of America.