Parker Bros. could, and would, make a set of 20-gauge barrels to fit a 2-frame 12-gauge gun. This 1889 vintage gun weighs a bit over nine pounds with the original 12-gauge barrels in place --
and 8 pounds 4.5 ounces with the 32-inch long, 3-inch chambered, 20-gauge Vulcan Steel barrels made some time between 1918 and 1926 in place.