While the database above provides general guidelines, the definitive source for Iver Johnson research is:

Before you can begin your research, you must locate the correct, complete serial number. A common mistake is looking only at the visible number on the trigger guard or butt. The key to accurate identification lies elsewhere.

These are derived from Goforth’s research and collector logs. They apply to (not the solid-frame “Trailsman” or late-model automatics).

Used for later models, where each prefix has its own chronological chart . 3. Barrel Markings

Similar to the first model but with minor design improvements to the action. Third Model Safety Automatic (1909–1941)