While the 1926 Ithaca Gun Co. catalogs oddly stated the 20-gauge was chambered for 2 1/2-inch shells, from the 1927 catalog onward the 20-gauge was listed with 2 3/4-inch chambers. I said oddly because the 1924 and 1925 Flues era Ithaca Gun Co. catalogs stated the 20-gauges had 2 3/4-inch chambers!?!