We recently wrote an article on the difference between .223 vs 5.56 and it sparked a similar question of what the difference is between .308 vs 7.62? Good question! Let’s go through what makes them different from each other so we can put this question to rest as well.
The .308 Win, or Winchester, was released by Winchester Ammunition in 1952. It was derived from the .300 savage cartridge that was developed in the 1920’s as the first high-intensity centerfire cartridge that was designed for the short action rifle. The .308 cartridge is a rimless bottleneck that was introduced to the commercial hunting industry in the 50’s and has since become the most popular choice for big game hunting worldwide. The caliber is available in a range of weights from 100 grains to 240 grains.
Two years after the release of the .308 Win, the 7.62×51 NATO round was introduced. It was developed as a standard for small arms among NATO countries, and later adopted in the M14 and M60 machine guns for U.S. service in the late 1950’s. As the successor of its .308 parent case, there has always been confusion over the differences.
Contrary to popular belief, the .308 and 7.62×51 are not the same. Although the dimensions of the two are basically the same, the differences lie in the chamber length and case thickness.
Look at the image below, one of the main differences between the two is their chamber length. The top image depicts a military rifle chamber while the bottom depicts a commercial rifle chamber. The dotted line represents the point on the shoulder where the cartridge would headspace. As you can see, there is a .013″ difference in chamber length. Most military rifle chambers will be longer.
A difference that can’t be seen from the external dimensions includes the case wall thickness. In general, military brass it thicker. So quite simply put, compared to a .308 the 7.62 has thicker case walls because military brass is made to stretch and function in a wide variety of chambers. Also the importance of thickness comes into play because full auto weapons don’t like thin wall cases.
Similar to the case of the .223 vs 5.56, there is a lot of confusion about whether it is safe to fire .308 out of a 7.62 chamber and vice versa. No one really gives a straight answer on this, but the general consensus is because the commercial ammo tends to be a little hotter than the military ammo (around 12,000 PSI), you can shoot 7.62 in a .308 chamber without much reservation, but the opposite isn’t as recommended. If you want to shoot .308 out of a chambered 7.62, make sure the firearm is marked to be able to do so, and if it doesn’t, check the head space using .308 commercial gauges.