As everyone knows, the .500 Jeffery started out as the 12,7x70 Schüler. All known prewar “.500 Jeffery” cartridges were made in Germany by Dornheim („Gecado“). John “Pondoro” Taylor wrote: “… the Jeffery .500, the ammunition for which was only obtainable in Germany.” The metric chamber, cartridge and barrel dimensions as well as the max pressure were all published with the German 1940 proof law. The 1940 RWS handbook listed it with a 534 gr steel jacketed bullet and 108 gr Rottweil R5 smokeless powder for a mv of 2490 fps from a 27.5” barrel, pressure 3200 at (copper crusher). Most likely the cartridge was never loaded using British Cordite. The only prewar original Jeffery rifle I encountered has a Schüler chamber.
This was the state of affairs until Mr. Little mixed things up when Kynamco started production. Instead of working with the long established and CIP registered 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 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 a much shallower shoulder angle (for ease of manufacture?) on their cartridge drawing. (remember, British chambering/ cartridge dimensions were often quite sloppy in pre-war times.) The dire results are:
1) There are now two sets of different dimensions for the 12.7x70 aka .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 dimension cartridges will not go into Mr. Little`s chambers.