The introduction of progressive burning smokeless powders, such as DuPont Oval, to shotgun shells in the early 1920s, allowed the ammunition manufacturers to move a 1 1/4 ounce load of shot out at a higher velocity than previously possible with the existing bulk or dense smokeless powders, and do it at lower pressure. According to DuPont Smokeless Shotgun Powder bookelets in my library, and a load of ammunition company catalogues from 1903 on, the heaviest loads offered by the North American ammo companies in 12-gauge 2 3/4 inch and longer cases was 3 1/2 drams bulk smokeless powders (DuPont or Schultze) or 28-grains of dense smokeless powder, such as Ballistite, and 1 1/4 ounce of shot. According to the DuPont booklets, these loads developed 11,700, 11,800 and 12,600 pounds pressure. Their new DuPont Oval progressive burning smokeless moved that 1 1/4 ounce of shot out at a higher velocity and only about 9600 pounds.
In some of my old sporting books from the early 20th century, the authors mentioned that they thought the 3 1/2 dram, 1 1/4 ounce load was too hot and advocated the 3 1/4 dram 1 1/4 ounce load as the max 12-gauge load.
At any rate, I'm sure in my mind that the metal of the HE-Grade Super-Fox is plenty strong to hold modern SAAMI spec shells, but is the 70 to 90 year old wood in the head of the stock up to the recoil of heavy payloads at high velocity? In the 1960s to 80s, I shot lots of 1 5/8 ounce 3-inch magnums out of my Super-Fox. When I first got it in 1963, it came with 2 1/2 boxes of pre-WW-II Remington Arrow Express 1 5/8 ounce 3-inch loads. So, this 17 year old never thought a thing about shooting the 1 5/8 ounce, and heavier, loads from it. I shot quite a few patterns with the gun and found it shot super tight patterns with the 1 5/8 ounce loads of #4 or #5 shot, but when I tried the 1 7/8 ounce loads I got holes in the patterns I could throw my Brittany through. That at least kept me using the 1 5/8 ounce loads as my heaviest.
Actually, the 12-gauge 3-inch MAGNUM shell with 1 5/8 ounce of shot didn't come out until 1935 when Winchester/Western introduced it along with their Model 12 Heavy Duck 12-gauge pump gun for 3-inch shells.
