The 3-inch
Magnum 20-gauge was a 1950s item. I think the first commercial listing was the Magnum Model 21 in the January 2, 1954, Winchester catalogue. However, there are no 3-inch 20-gauge shells listed in the January 2, 1954, Winchester Ammunition catalogue and price list!?! The Olin brothers and their buddies had been playing around with 3-inch 20-gauge Model 21s for some time before that. In the 1955 Winchester ammunition catalogue the 20-gauge 3-inch Mag. is offered with 1 1/8 ounce of Lubaloy #6 or 1 3/16 ounce of Lubaloy #4. That same year the 2 3/4 inch "magnum" shells were introduced with the 1 1/2 ounce in 12-gauge, 1 1/4 ounce in 16-gauge and 1 1/8 ounce in 20-gauge. The 3-inch 20-gauge Mag. offerings remained the same throught the 1959 price list. For 1960 the 3-inch 20-gauge magnum with 1 1/4 ounce of chilled shot was added to the offereings, while the Lubaloy loads were still 1 1/8 and 1 3/16. The Winchester/Western offerings in 3-inch 20-gauge shells remained the same thru 1968 where my old catalogues play out.
Three-inch shells have been around just about as long as cartridge shotguns have been around. In my 1903 UMC catalogue there were 12-gauge paper shells 2 5/8, 2 3/4, 2 7/8, 3 and 3 1/4 inch. The 16-gauge was available 2 9/16, 2 3/4, 2 7/8, and 3 inch. The 20-gauge was offered in 2 1/2, 2 3/4, 2 7/8, and 3 inch. In those days the "standard" 2 5/8 inch 12-gauge, 2 9/16 inch 16-gauge and 2 1/2 inch 20-gauge shells carried a slightly milder maximum load than the 2 3/4 inch and longer shells. The advantage of the 2 7/8, 3 and 3 1/4 inch shells was more and better wadding for a better gas seal which many serious Pigeon shooters thought to be an advantage. The heaviest loads offered in the 2 1/2 inch 20-gauge shells were 2 1/4 drams of bulk smokeless powder pushing 7/8 ounce of shot, or 18 grains of Ballistite or Infallible dense smokeless powder pushing the same 7/8 ounce of shot. In the 2 3/4 inch 20-gauge case, one could get 2 1/2 drams bulk smokeless powder or 20 grains of Infallible or Ballistite dense smokeless powder, but still pushing 7/8 ounce of shot. The 3-inch 20-gauge for the famous Widgeon Duck Club Parker Bros. guns and the J. Stevens A & T Co. pump gun carried these 7/8 ounce loads, but more wadding.
These are the shells a Parker Bros. 20-gauge chambered for 3-inch shells with serial number 131424 would have been made for --
Same load in a 2 7/8 inch shell --
And, the same load from Peters Cartridge Co. --
When Western Cartridge Co. showed the way to high velocity by introducing progressive burning smokeless powder loads as their new Super-X load about 1922, the 1 1/4 ounce 12- and the 1 ounce 20-gauge Super-X loads were put up in their 2 3/4 inch Field shell. It doesn't appear from my research that Winchester, Western or Remington offered their progressive burning powder 20-gauge shells in longer cases, but in the 1920s and 30s Peters Cartridge Co. did --
