You have bought a very nice example of long barrelled 11.3 mm Gasser M1870 "Montenegrin"
) revolver. This old baby is able to fire a .446" lead bullet of up to 313 grains to the target with remarkable accuracy and devastating results (equal or slightly superior of the .45 Colt or .44 S&W Russian). You are most welcome to view many excellent, thorough and well founded historical and technical observations on this remarkable antique revolver on www.luger.gunboards.com
under the special topic: "Gasser M1870 11mm revolver".
If you are interested to reload somme obsolete 11.3 mm Montenegrin ammo you may use BLACK powder
(NOT any kind of smokeless powders, as the specific revolver is made by the milder and not so strong cast steel - aka GUSS STAHL), along with 11.75 mm Montenegrin hulls
made by "Bertram Bullet Co"
in Australia (available for sale in the U.S. market by "Midway USA"
), .439" - .446" lead bullets,
weighting 465, 370 and 370 grains respectively, which can be easily produced by melted lead after using the Bullet Molds # 446187, #439187 and #439186
made by "General Ordnance Development"
in U.S.A. . Good luck with the new baby and let us kmnow your test firing results ...