Experimental cartridge designed by CETME (Centro de Estudios Tecnicos de Materiales Especiales – Special Materials Technical Studies Center) in 1953. The case is slightly longer than the original 7.92 X 40 CETME. During the development of the CETME rifle, it was decided by CETME to also experiment with a .30 cal. cartridge with a shorter case and therefore lighter charge. The main aim of this experiment was to increase the manageability of the rifle during full auto fire. The designs were based on the earlier 7.92×33 KURZ although the 7.92 CETME M53 cartridge was a little more powerful and had a 40mm case. This cartridge was necked down to .30 cal. and was identical to the 7.92 except for the bullet diameter.

This apparently happened as a mistake. Dr. Ludwig Vorgrimmler, who was an engineer at Mauser during WW2 helped the Spanish company CETME improve the designs of the experimental 7.92 x 40 cartridge. During the early 1950’s work was done by NATO in the development of the 7.62×51 NATO but the Spanish were not fully integrated into that research at that stage. The Spanish were however interested in the CETME designs as was the West German Border Guards (Bundesgrenzschutz). Germany being the youngest member of NATO at that stage did not have any leeway in decision making regarding all the new military hardware and basically take what NATO gave them. They therefore specified to the Spanish that their design must be of 7.62mm design and neither they nor CETME checked that the request was actually for the 7.62 x 51 cartridge and CETME developed the 7.62 x 41 CETME that was a necked down version of the original.

Early CETME assault rifle prototype chambered for experimental 7.92x40mm cartridge