The locking bite at the back of the rear lump is similar that that used in John Thomas’s British patent 324/1870 but that is held down by a rotating turret. It was quite popular, often being found on rook rifles and small gauge shotguns.

I have looked in Crudgington and Baker Volumes 1 and 2 which cover 1850 to 1890 but there is no mention of Sherman’s patent.

I wonder if he decided to get W.C. Scott to build it for him as a demonstration gun?