If it is a Browning Superposed 12 gauge it was made in 1959.
This gun was made in 1970
You can, but, you will cause a barrel bulge after a while.
Try the gunpartscorp.com
100-10000 usd
The Dictionary says: "to place above or upon something else, or one upon another." As in the case of the Browning shotgun, the Superposed model ws the first sucessful Over/Under shotgun ever made. Browning used the dictionary description to name the model "Superposed" because one barrel is apon another.
In order to answer your question I would need to know if your shotgun is a auto-5,browning pump shotgun(BPS) or a over-under(CItori or superposed)to give you a accurate answer?
You will have to get it lettered by Browning.
100-2000 usd
The browning superposed lightning trap shotgun will command a nice price.If your shotgun is between 60%-90% in its original finish and a good set of bores,you can get between 700-1,000 dollars.
This gun if a Superposed was made in 1956. It is most likely a Superposed. Superposed shotguns are very collectable when in top condition. Values have a wide range due to so many variations and grades of the Superposed and other Browning Over/Unders. Value is too difficult to be accurate without seeing the gun. Condition which includes the amount of original finish and original configuration will determine value. Recommend taking it to a gun shop for appraisal.
A Browning Superposed shotgun is a very high quality over-under double barrel originally made in Belgium for the Browning company. A Presentation Grade gun is a very lavishly engraved gun, possibly decorated with gold inlays, with a finely checkered and/or engraved stock of fancy select-grade walnut. It would be boxed in a fitted, velvet-lined wooden case. It would typically have been well cared for and in excellent condition to preserve its value, which would likely be at least 8-10 times higher than a Field grade Superposed.