Browning, Mid West Gun Works, Brownell's, are places to start.
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.
You will have to get it lettered by Browning.
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?
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A Browning Superposed shotgun is a very high quality over-under double barrel originally made in Belgium for the Browning company.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.