I also found this in a circa 1937-8 Winchester shot shells folder --
3-inch 12-gauge and Model 12 Heavy Duck 1938 folder.jpeg
which doesn't call either load MAGNUM.
Western Cartridge Co., which owned Winchester, did call the heavier load MAGNUM in all their listing I've looked at from this December 24, 1936 --
Super-X December 24, 1936, cropped.jpg
to 1953. Beginning with 1954 price lists, both Winchester and Western began calling all the 12-gauge 3-inch loads MAGNUM?!?
I don't have much Peters Cartridge Co. paper, but this March 13, 1947, Peters catalog list the 1 5/8 ounce load as MAGNUM --
Peters De Luxe Target March 13, 1947.jpeg
Hopefully this will conclude my sermon on 12-gauge 3-inch progressive burning powder load inconsequential trivia!
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