Here are some notes from my database on the 9.3x75R Nimrod:
*********************Produced from c1905
This scarce calibre is a bit of a mystery and was not shown in any known catalog but an RWS factory drawing (dated 18.7.1930) of this cartridge exists. Examples exist with either the proprietary “NIMROD-GEWEHRFABRIK SUHL” or the probably newer but still pre-1922 “9.3X75 * NIMROD *” hs , both of which are likely to be of RWS manufacturer. This is sometimes confused for the 9.3x74R Mauser (M60).
This case, like the other Nimrod 9.3mm types (EXP14, EXP16) has a very slight neck and the case tapers consistently from the base with a diameter of 11.0mm to the start of the neck at a diameter of 10.1mm (ie a 1.1mm taper over 66mm of case). This is a more gradual taper than most other 360 based German Express types.
Riim thickness appear to vary from 1.1 to 1.25mm (like an “E” type) and range from squared edge to bevelled, which gives a false impression of a narrower rim than it actually is. Unlike the 9.3x82R Nimrod, this has a narrower rim diameter (specimens vary from 12.25-12.4mm).
Most examples of these appear to have the bullet seated lower than one would expect which gives an overall cartridge length very similar to the loaded 9.3x72R Nimrod type (EXP14). Maybe they were intended for the same weapon ??
Meyer’s Panorama des Munitions lists a “GECADO + * +” hs example which appears to be this case type and would indicate GECADO production. Horneber also produced cases c2004-2005.
*More recently Horneber produced this case type with no h/s.