We haven’t done a Historical Intermediate Calibers post in a while, mostly because most of the stuff that’s interesting enough to cover is difficult to find real world examples of. Today, we’ll be looking at one round I had planned to do ever since the series expanded beyond the original seven rounds covered, but of which I hadn’t been able to find a physical example until recently. Most of what I’ll call “first generation” intermediate rounds (although they aren’t truly the first) owe some debt to the German 7.92×33 Kurz caliber developed in Nazi Germany, but today’s round is truly its heir. After Nazi Germany’s capitulation in World War II, Mauser’s engineers fell into the hands of the French government, who set them to work developing weapons for French forces, including carbines based on the roller retarded blowback StG-45 assault rifle. Unhappy with his work in France, Ludwig Vorgrimler, who had worked on roller blowback firearms since before the Nazi surrender, left the country in June of 1950 and moved to Spain, where he began working for the Spanish Centro de Estudios Technicales de Materiales Especiales (CETME), who were responding to an ambitious Spanish military requirement for a new assault rifle. The weapon had to be less than 7 pounds in weight, controllable in the fully automatic fire mode, and have a maximum range of 1,000 meters. To meet this requirement, a former Luftwaffe ballistician named Dr. Gunther Voss came up with a unique idea: A new projectile with an aluminum core and gilding metal cladding, which would be very lightweight, yet very long and with a relatively high ballistic coefficient. The gilding metal cladding was ingenious, as it gave the bullet high rotational inertia, similar to a flywheel, which ensured it would remain stabilized throughout its flight, despite its extreme length.
I do not have data for the ballistic coefficient or form factor of the resulting 105gr (6.8g) 7.92mm CETME bullet, so the data below is an educated guess on my part using an estimated 0.76 i7 FF, which is exceptionally good. Anecdotally, this bullet was supposed to have a ballistic coefficient similar to the 7.62mm NATO’s projectile (0.200 G7), which suggests this estimate is essentially correct.
On to the graphs:
These graphs indicate that the Voss bullet concept did exactly what it was designed to do. With respect to velocity, drop, and drift the 7.92×40 CETME dramatically out-performs the 7.92×33 Kurz, and nearly matches the 7.62x51mm NATO. Only with respect to energy does the CETME round fall short of the 7.62mm, although it still performs better in this respect to either the 7.92×33 Kurz or the modern 5.56mm M855.
In terms of weight, the 7.92×40 CETME scores well, being every bit as light as other brass cased full-caliber “Kurz” type rounds, at 17.5 grams per shot. It does not, however, compare well in this respect to more modern SCHV calibers like the 5.56mm, which weigh 12 grams per round.
The rifle that Vorgrimler designed and that fired the 7.92×40 CETME lived on and became what is known today the “CETME rifle”, and which was also slightly modified to become the world-famous Heckler & Koch G3. The caliber itself, however, didn’t, nor did its innovative flywheel-esque stabilization concept. A very similar idea would crop up again later, though, with the 5.56x38mm FABRL round developed by Frankford Arsenal in the 1970s.