Help IDing some British and European firearms

[RDGAC]

Next up, what I am fairly sure is an M1874 "Montenegrin" Gasser revolver, though I can't as yet find out who made it. Reasonable condition, but reluctant to dry fire; the hammer cocks smoothly but the trigger doesn't appear to break. Some slight pressure on the hammer spur will, however, release the hammer. Sadly de-activated; I say sadly because I can't imagine that an 11.2mm black powder cartridge not used since the Great War could not be on the obsolete calibres list.