The true, Parker "12-gauge 3-inch Magnum" guns are all late Remington guns. Parker Bros. would always chamber a gun for longer shells throughout their years, but back in the day, our North American ammunition companies didn't put heavier loads in the long shells (2 7/8, 3 and 3 1/4 inch) than one could have in a 2 3/4 inch shell. The long shells got more/better wadding. The progressive burning powder, high velocity, 12-gauge 3-inch shell with 1 3/8 ounce of shot hit the market in the 1924/5 time frame --
The 12-gauge 3-inch
Magnum loads with 1 5/8 ounce of shot were introduced in 1935 by the Olins along with their new Winchester Model 12 Heavy Duck gun.
