Does there appear to be any other tools or mechanisms with a similar looking age, design or Metallurgy? Whatever it is, its incomplete, and its hard to judge without any context.
I suspect it could have been either a customer tool for a specific purpose, or an attempt a custom project that never got finished. I expect as a gun smith curiosity might have struck him one day and he tried to design/fabricate something, and then got busy with paying work and never finished it.