Though there were once at least six differently shaped cartridges with that caliber and case length, five of them based on the Mauser M71 MB base, all of them were obsolete before 1900. As Philip Reeb set up under his own name in 1911 at the same Bonn address as his J.J.Reeb family business. such a chambering is not very likely. You will not get around making a chamber cast to establish bore, base, rim and neck diameters as well as shoulder position and rim recess depth. Also, please post photos of all markings on and under the barrels. Anyhow, you will have to make the cases yourself. Only with all informartion available it will be possible to recommend a basic case and bullet source.