Iver Johnson Champion 12 Gauge Single Shot Shotgun Disassembly -

But even a champion needs a bath. If you’ve acquired a rusty, gummed-up heirloom or just want to give your old-timer a proper cleaning, disassembly is straightforward— provided you know the one hidden trick that frustrates most first-timers. SAFETY FIRST. Open the action. Visually inspect the chamber and barrel. Stick a finger in there. Make sure it is empty. Then, do it again. This shotgun has a hammer that rests directly on the firing pin; there is no transfer bar on most models. Assume it wants to fire.

If your Champion is pre-1940 with a "two-piece" firing pin, do not dry-fire it. You will break the firing pin. Use a snap cap or a spent shell. But even a champion needs a bath

You will feel a solid thunk . The entire barrel assembly will slide forward off the receiver about an inch. Lift it up and away. Congratulations: you now have a two-piece shotgun. Flip the receiver over. You’ll see a flat metal plate held by one or two small screws. Remove these. The entire trigger plate—containing the trigger, hammer, sear, and mainspring—will now lift out as a single cassette. Open the action