Believe that will be a shotgun, not a rifle. Made by Crescent for distribution by HD Folsom around 1890-1910. Value is minimal, well under $100. Dont attempt to shoot it. sales@countrygunsmith.net
1000 uSD
No published sn data that I know of.
DO NOT ATTEMPT TO FIRE IT UNTIL IT IS CHECKED OVER BY A COMPETENT GUNSMITH!!!
Contact Ruger
American Gun Co was a trade name used by H&D Folsom, usually found on single and double barrel shotguns c. 1880-1920. The company began operation about 1860 so it is quite possible that they would have distributed some muzzle loaders. I can't find anything about J Gebhard on Google. I suspect was a hardware store in Ft Wayne Indianna, but the original owner could have had his name engraved on the barrel.
You can find information for the 16 gauge Worthington Challenger single barrel shotgun at most gun stores and pawn shops. Many of these stores offer free appraisals and have knowledgeable clerks.
Double barrel? Single barrel? Model? Need more information in order to be able to answer.
Trade name, 50-100 USD
Blue Book of Gun Values
nitro hunter shotgun single barrel with exposed hammer stamped belknap hdwre and mfg serial 5516
Store brand from turn of the century. Little value.
Probably early part of the century.