That revolver looks to belong to the general class called "Montenegrin revolvers", of which Gasser was a major maker.* (Many were also made in - where else? - Liege.) But the smallest cartridge identified with the Montenegrin revolvers is 10.8mm, too large for your revolver.
The 9mm Austrian service cartridge (sometimes called the 9mm Gasser) had a bullet only about .362" (9.2mm) so a 9.5 mm cylinder bore would seem oversize. I can't really find any likely cartridge that would match that figure either. Maybe a chamber cast would help identify the cartridge.
*The story is that King Nicholas First (and last) of Montenegro ("Black Mountain") ordered every male suibject to buy and carry a large calilber revolver. Reportedly His Majesty got a kickback on every revolver sold in the Kingdom. The 11.3mm is the most common of the class. After WWI, the country became part of Yugoslavia, but since 2006 has been an independent republic.
Jim