I've got a 20-gauge VH-Grade, 0-frame gun that was shipped in 1930, and it has 2 3/8 inch chambers intended for the 2 1/2 inch 20-gauge shells.
The "Standard" North American 20-gauge shell throughout the first quarter of the 20th Century was 2 1/2 inch, and the vast majority of American 20-gauge doubles were chambered for that shell. The 2 1/2 inch 20-gauge shell of those days carried a maximum load of 2 1/4 drams of bulk smokeless powder (DuPont, E.C., Schultze, Empire, Wolf, Mullerite, etc.) or 18-grains of dense smokeless powder (Ballistite, Infallible) or 24-grains of Walsrode and 7/8 ounce of shot. Longer 20-gauge shells were offered at extra cost in 2 3/4", 2 7/8" and 3". The long shells advantage was more and better wadding for a better gas seal, and a slightly hotter/faster load. In the 20-gauge they were offered with a slightly hotter/faster load with 2 1/2 drams of bulk or 20-grains of dense smokeless powders (Ballistite or Infallible) or 26-grains of Walsrode but still with only 7/8 ounce of shot.
All the manufacturers would chamber for the long shells upon request at no extra charge in a new gun. Back in those days the chamber length usually wasn’t marked on the guns and the only way to know for sure is if the original hang tag or factory records still exist.