there are no known serial number records available for iver johnson single barrel shotguns. it has been my experence that the iver johnson champion single barrel shotguns with a single letter code suffix were manufactured in the late 1920's early 1930's. patent date 1-15-1916 is for number 1142934. this patent is for a method of mounted a small bore barrel on a standard size frame.
the barrel markings should read "410 Gauge, Choke Bore, Barrel and Lug Forge in One" yes iver johnson did use the word gauge with some of their 410 bore guns.
the reciever should be marked Iver Johnson's Arms & Cycle Works Fitchburg, Mass. U.S.A. CHAMPION
serial number should be on the tang behind the trigger guard.
these are the markings as they appeared in catalog number 27A (used in the years 1928 & 1929. catalogs before that the champion name was not marked on the reciever. bill