From an older IAA Forum post: – These are calibre reduction experimentals for a Remington breech-loading rifle proposed by a Danish designer whose correct name apparently is Adolph Keifler, but also written as “Koifler”, “Koiffler” and “Koeffler”. Information about them can be divided into three categories: Cartridges described in reports, cartridges identified as “Keifler” in an old collection, and cartridges believed to be Keifler experimentals. As far as could be ascertained, the first category comprises only one single cartridge of 8.5mm calibre that was tested by the Austrian government in 1882. It is described as having a rimmed case made of brass, flat primer, a load of 5g (77 grain) of Rottweil powder, and a paper patched lead bullet weighing 15.7g (242 grains). It was discarded because it was inferior in performance to the 11 mm Werndl M. 1877 cartridge. The second category involves two different cartridges: a 9x36R with straight case and no headstamp that is labelled “J. Koiffler 9 mm Projekt Patrone”, and a 9.3x59R with bottlenecked case and Roth 1886 headstamp that is labelled “Ing. J. Koiffler”. The first one could be an experimental for a Danish Remington rifle proposed by Keifler in 1870 (tested in Austria) and the second, according to Mötz comments, would be too late for a calibre reduction experimental and presumed to be a “sporting experimental”. This specimen below is dated 1883, so it might possibly still be the correct time period. The third category is based on the conjecture that a calibre reduction from the early 1880’s could be a Keifler experimental cartridge. The list includes: 9x58R made by Seraphin Keller in 1883, 9.3×63.5R made by Roth in 1882 (same bullet as the 9.3x59R) and 8x50R also made by Roth in 1882.
According to leading authority on the subject, Josef Mötz, The only real source for the Keifler or Koiffler cartridge is an old Austro-Hungarian Military Journal (Mittheilungen über Gegenstände des Artillerie- und Genie-Wesens (MAG)) of 1884, pp109: Gewehrpatrone System Keifler Kal. 8,5 mm, flaschenförmige Messinghülse, 5 g Rottweiler Pulver, Geschoss Weichblei Papierführung 16,7 g, v0 508 m/s.