Just in time for the introduction of the Western Super-X. This Western Cartridge Co. ad in the October 1922,
National Sportsman is the earliest I've found discussing the Super-X load --
Ad introduces 16-ga Super-X load in Field Shell Oct. 1922, National Sportsman.jpg
This ad introduces the 16-gauge Super-X load. I suspect there are earlier ads for the Super-X load, but I've yet to find them.