Identifying an unusual rifled breechloader

What can be established about the unusual gun shown in the submitted photographs?

The photographs suggest a low-pressure rifled shell gun with possible French influence, but do not establish its identity.

The apparent breech mechanism, rifling and unusually placed barrel reinforcement suggest an early or unconventional design. The small breech also raises the possibility of a composite assembly. A low-pressure gun related to a French rifled shell-gun concept is one tentative identification. Measurements, markings and direct inspection would be needed to distinguish an original design from a copy or derivative.