I was looking in the spring 2015 Hermann Historica auction catalong and there was another Volley gun this time a Vierling made by Johann Haberda, Schloss Frauenberg (Hluboká), Böhmen 1880
proably made for the 320 CF revolver cartridge it looks like you can fire 2 or 4 barrels at once
engraved with "PATENT HEISSIG" and "JOH. HABERDA, FRAUENBERG, BÖHMEN / FÜRST. SCHWARZENBERG'scher HOFBÜCHSENMACHER."

http://www.hermann-historica.de/db2_de/auktion-70.html