The name Superposed refers to one barrel being Superposed over the other one.
There have been shotguns for centuries, but only good shotguns with two barrels laid side by side for about two hundred years, that were light enough and dependable enough that men could shoot first one, and then another fast flying birds. The first good sorting doubles were the ones made by Joe Manton, and later on a bunch of other makers supplied wealthy men with fine side by side sporting double shotguns.
After the American Civil War the perfection of the break open cartridge side by side double gun, by the Parker Brothers as much as anyone else, drove the price of a usable fine double gun down from about $100 to about $25, and Belgian made clunkers only cost $10.
John Moses Browning then designed first the Winchester 93/7 pumps and his magnum opus masterpiece the Auto Five (Remington 11 over here) and by the 1920s the American (and other) markets were flooded with such efficient, useable, modern double and repeating shotguns any of which are still usable today (and we shotgun addicts do use them).
But all around and all over the world around, every gun maker was tooled up to produce side by side doubles or pump or automatic repeating shotguns. The English best gun makers made a few double guns with Superposed barrels, at princely prices.
So just before his reputed death, the great JMB started developing a modern over and under shotgun his surviving son Val Browning lived to market, as a Superposed. It cost only about $100, had a fore end that did not remove when the gun was broken into pieces, and a double single trigger that worked, most of the time.
Remington responded with their Model 32, which in due time became the Krieghoff K-32, after the Germans learned to not start wars which ended in their utter defeat.
And, seeing how bombing Pearl Harbor only brought a rain of atomic ruin on their home islands the Japanese started making copies of the Browning Superposed in the early 1960s, and to this day a sportsman with about $100 of 1931 money ($1,771 today) wants a stack barrel shotgun as close to a real Superposed as he can find.
Genuine FN made Browning Superposed shotguns are still available from FN. They cost $25,000 for the basic gun, engraving is extra, and there is a two year wait.
The finest Superposed shotguns were made from the early fifties until economy measures were begun about 1966.
Even the field models of the fifties and early sixties are engraved my masters, wood is exquisite, and after 1938 the single selective triggers are foolproof.
A perfect 12 gauge standard field grade specimen of a Superposed made in the glory years was about the price of a new Citori before the plague of Corono hit the world.
A Superposed does not and will never handle steel shot. The chambers rust while you watch them, in the rain. The presence of a recoil pad usually severely depreciates the piece. They aren't for everybody.
But I just love em'.
The single sighting plane makes every miss due to the need for more practice.
And, you can't lose the fore end, either.
All thanks to the immortal JMB stacking the barrels on top of each other and Val Browning giving his Father's last design (other than the 1935 Hi Power) a market five years after some claim the Great Gun Prophet died, is the reason why, we mortals were blessed with the Superposed.
Others claim that JMB ascended on the wings of caroling angels to a far better land, but who can say, all these years later.