The NID Magnum-Twelve first appears in the retail price list in the 1937 Ithaca Gun Co. catalogue, but doesn't appear in the text until the 1938 catalogue where it says "Magnum 12 gauge, 30 inch barrels. Chamber length 3 inches." and "Magnum 12 ga. for 3 in. shell, about 8 1/2 to 9 lbs." Those I've handled are all of that and more!!
The original Western Super-X 3-inch 12-gauge shell carried a 1 3/8 ounce load. The Super-X 12-gauge 3-inch Magnum load with 1 5/8 ounce of shot came out along with the Winchester Model 12 Heavy Duck gun in 1935.
