This is my pelter (shoots pellets/shot) - a 20 bore custom single by Hunkeler in the USA: Not a copy of any gun - just a generic smoothbore, of English or New England pattern. IC choke - shoots modified patterns with 2 1/2 drams 2F and 1oz. shot.
28 yard, 5 shot group from a bench, using 3 drams (82gr.) 2F and a .595" round ball, + of course, a decent patch. Too bad it has a flyer.