A rare 19th century market gun is valued at $8,000-12,000 ahead of a sale of firearms at Morphy Auctions in Denver.
The weapon was invented for hunting waterfowl, primarily on the Susquehanna River in Pennsylvania.
The auction house explained: "The large size of these guns made them literally small cannons which were mounted to the gunwales of the punt boat, which was a square shaped flat bottomed boat which was pulled in close to duck or geese flocks quietly until within range.
"Once the piece was fired it could often kill several dozen birds at one firing."
After this practise was outlawed the majority of the guns were destroyed, making those that remain highly desirable.
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