As everyone knows, the .500 Jeffery started out as the 12,7x70 Schüler. All known cartridges were made in germany by Dornheim („Gecado“), see Taylor:"African Rifles and Cartridges".
This was the state of things until Mr. Little mixed things up when Kynamco started production. Instead of working with the long established and registered CIP dimensions of the 12.7x70 Schüler, he decided to reinvent the wheel. Apparently he worked from an obscure drawing of a cartridge from the Kynoch archives (the original Kynoch company had never sold such a cartridge!), designed chambering dimensions around it and registered the whole shebang as the „proper dimensions“for the .500 Jeffery. Now Kynoch had put an much shallower shoulder angle (for ease of manufacture?) on their cartridge drawing. (remember, British chambering/ cartridge dimensions were purposely sloppy in pre-war times, see f.i. the military .303 rifles). The dire results are:
1) Thereare now two sets of different dimensions for the .500 Schüler and the .500 Jeffery.
2) Kynamco`s cartridges will work ok in an original or Schüler chamber (with a lttle bit of fireforming the shoulder area), but original or Schüler cartridges will not go into Mr. Little`s chambers.