Pivi, these are caliber 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 I know, first category comprises only one single cartridge of 8.5 mm caliber 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 5 g of Rottweil powder, and a paper pacthed lead bullet weighing 15.7 g. It was discarded because it had inferior performance that the 11 mm Werndl M. 1877 cartridge (11.2x58R).
Second category involves two different cartridges: a 9x36R with straight case and no headstamp that is labeled “J. Koiffler 9 mm Projekt Patrone”, and a 9.3x59R with bottlenecked case and Roth 1886 headstamp that is labeled “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 caliber reduction and presumed to be a “sporting experimental”.
Third category is based on the conjeture that a caliber reduction from the early 1880’s could be a Keifler experimental cartridge. List includes: 9x58R made by Seraphin Keller in 1883, 9.3x63.5R made by Roth in 1882 (same bullet as the 9.3x59R) and 8x50R also made by Roth in 1882. There are other examples that may fall into this category but I have not seen them listed as “Keifler”.