Like Kabar2 I was intrigued by Shooter2’s mystery breechloader at Washington Navy Yard. A friend dug out John C. Reilly’s 1991 book “The Iron Guns of Willard Park: Washington Navy Yard.”, which describes most of the pieces there. According to Reilly there are no marks at all on the breechloader and no clue in the Navy Yard as to who made it or where it came from. He speculated that it was made to Joseph Needham’s patent of 1867 with a “horizontally rotating cylindrical breechblock”.
Looking out the patent and its earlier English original, that seems to fit the description, the breechblock swings out sideways from a pivot at the “cascabel” end, but it was created for rifles and muskets, not cannon. Has anyone else come across pictures or a description of the mystery breechloader and how it works? And who made it?