#7.62x40

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.

Like the .300 AAC Blackout that we discussed earlier, the 7.62×40 Wilson Tactical was intended to be a medium-performance .30 caliber cartridge that would function in standard AR-15 type rifles with minimal modifications, such as a barrel change. Also like the .300 AAC Blackout, the Wilson round was based on an earlier wildcat, which was designed by Ken Buchert and also called the 7.62×40. Unlike the .300 Blackout, however, the 7.62x40mm Wilson Tactical sacrificed some versatility for raw power in the form of a lengthened case based on the 5.56mm case, instead of the .221 Remington Fireball used by the Whisper/Blackout. This longer case gives the 7.62×40 WT a significant performance advantage over the .300 Blackout from comparable barrel lengths, but it limits how ballistically efficient the projectiles used by the round can be. In theory, the 7.62×40 WT can also be loaded with subsonics, like the .300 AAC Blackout, although the short ogive length limits which COTS bullets can be used for this, and no factory subsonic ammunition exists for the Wilson round. This makes the 7.62×40 WT virtually a dedicated supersonic hunting or 3-Gun round (in which it makes Major Power Factor), but it is still worth considering in our discussion. Now, on to the ballistics:

Despite coming out strongly for the .300 AAC BLK cartridge, Wilson Combat has developed their own 7.62x39mm-equivalent for the AR-15. The 7.62x40mm WT is a 5.56mm NATO cartridge necked up to .30 caliber. To convert an AR-15 to use the 7.62×40 WT a barrel change is (obviously) required and a special Wilson-modified version of Lancer’s L5 AWM polymer magazine.