It seems to have really taken hold in those grim Great Depression years when the makers were desperate to move some product any way possible. They may have picked up the idea from the early Western Super-X 3-inch 12-gauge boxes which carried the warning --
INTENDED FOR USE
ONLY IN SHOTGUNS THAT HAVE
3-INCH CHAMBERS AND
MODERN STEEL BARRELS
Early 12-gauge RECORD Super-X 3-inch.jpg