he 7.62 NATO and .308 Winchester cartridges have a long and storied history in the world of firearms. After World War II, the U.S. Army began experimenting with a new rifle caliber that would be shorter overall but perform comparably to the .30-06 Springfield, which had been used to great success in the war. This created the 7.62x51mm cartridge with a .30 caliber bullet diameter. However, due to inefficiencies within the Army, Winchester obtained the new cartridge dimensions and released the “308 Winchester” to the civilian market in 1952, two years before the Pentagon officially approved the 7.62×51.
In 1957, NATO officially adopted the American 7.62x51mm cartridge, which gave it the alternate designation of 7.62 NATO. This led to the U.S. troops being issued the newly adopted M14 battle rifle, also chambered in 7.62x51mm. Although the 7.62 NATO and .308 Winchester cartridges look almost the same, there are subtle differences between the two, primarily in terms of pressure capacity, case sizing, and chamber dimensions. It is important to note that the 7.62 NATO round has a “51” following the “7.62” designation, differentiating it from other cartridges such as the 7.62x39mm and 7.62x54R.
The history of 7.62 NATO and .308 Winchester
After the latter conflict, the “long action” .30-06 Springfield was successful in helping the U.S. military win two world wars in partnership with the M1903 Springfield and the M1 Garand. Still, it fell out of favor with the military after the latter conflict. Army following World War II. The Army wanted a new rifle caliber that would be shorter overall but performs comparably to the .30-06. The .30-06 caliber was being used and proved effective in Korea. The Army was experimenting with a different version of the .300 Savage, designated as the T65.
The cartridge size fluctuated before settling at 51 mm. A new 7.62x51mm cartridge with the .30 caliber bullet diameter translated as “7.62 millimeters” was created.
Big Army’s inefficiency led to a delay in testing and evaluation. Winchester was able to obtain the new cartridge dimensions during this time. In 1952, Winchester released the new “308 Winchester” to the civilian market, two years before the Pentagon officially approved the 7.62×51.
In 1957, NATO officially adopted the American 7.62x51mm cartridge, which gave it the alternate designation of 7.62 NATO. That same year, U.S. troops were given the newly adopted M14 battle rifle, also chambered in 7.62x51mm.
What’s the difference between 7.62 NATO and .308 Winchester?
The 7.62 NATO and .308 Winchester look almost identical, but subtle differences exist. The difference between the two types of boilers primarily comes down to three key factors: pressure capacity, case sizing, and chamber dimensions.
Ensure the number combination “7.62” is followed by a “51” instead of some other number when referring to the NATO round.
The original caliber of the AK-47 is 7.62×39. The .300 Blackout round is slightly similar to the 7.62×35 designation, and the standard Russian sniper round is the 7.62x54R. Need help keeping it straight? The “51” round from NATO entered service in the 1950s. However, it does not have the “R” for the “rimmed” Russian round.
Task & Purpose glossary for 7.62 NATO and .308 Winchester
Before we start discussing the technical details, let’s take a moment to define a few key terms that will make this conversation more straightforward.
7.62×39 v 7.62×51 v 7.62x54R: Cartridge Sizes
There is a big difference in case length, overall length, rim diameter, and case capacity between the 7.62x54R and the 7.62x39mm. Although the 7.62×39 and 7.62×54 have the same bullet diameter, they are different cartridges.
Other than the 7.62x54R, the other two cartridges are rimless.
The 7.62×39 and .308 Winchester cartridges are the only ones standardized by the Permanent International Commission for the Proof of Small Arms (CIP). Also, by the Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI). The .308 Winchester has the highest pressure rating as determined by CIP, compared to the 7.62x54R and 7.62×39.
Although the figures below show differences between the three cartridges, exact case capacities could differ slightly based on the brass in use.
7.62×39 vs. 308 vs. 7.62x54R Ballistics
The three cartridges – 7.62x39mm, .308 Winchester, and 7.62x54R – have different external dimensions, which results in different ballistics.
The 7.62x39mm has the distinction of firing the lightest bullet at the slowest speed and having the lowest ballistic coefficient. It has the least kinetic energy and a more arching trajectory.
The .308 Winchester and 7.62x54R have very similar external ballistics. Still, the .308 has a slightly flatter trajectory. Its extended range comes from the higher ballistic coefficient of the bullets, meaning more energy is maintained.
The 7.62×39 goes subsonic at 575-600 yards, the 7.62x54R at 875-900 yards, and the .308 Winchester at 975-1,000 yards.
The chart below illustrates the impact a 10-mile-per-hour crosswind has on three different loads out to 500 yards.
The 7.62x39mm bullet experiences more wind drift than the .308 Winchester load by nearly two feet at 500 yards. At long range, the .308 Winchester and 7.62x54R bullets will be affected by the wind similarly, with the .308 load slightly less due to its higher ballistic coefficient.
The chamber is the part of the gun where the bullet goes in before the gun is fired. Using the right kind of ammunition with this gun will position the bullet correctly to start its travel down the barrel. This article by Bison Ballistics provides a more detailed breakdown of chambers.
Headspace is the distance between the bottom of the case and the part that locks the cartridge in the chamber. The locking portion of the case will be different depending on the caliber. If there is too much headspace, the cartridges will be able to move around too much in the chamber. If there is too little headspace, the bolt cannot close correctly. These deviations from the SAAMI specifications can result in potentially catastrophic issues. If you want to learn more about headspace, “Cheaper Than Dirt” has an excellent article by Oleg Volk.
Screwing on the pressure
First off, let’s talk about force. Our M14s are structured so that when the trigger is pulled, it initiates a response that sends out the bullet. When pulling the trigger sets the firing pin into motion, which connects with the primer on the bullet positioned within the chamber. This sparks the propellant, thus propelling ahead the bullet.
The force of the chemical reaction is strong enough to send a tiny lead bullet flying up to a mile away, with only its base being the weakest part.
A thin-bodied brass or steel casing is capable of handling immense pressure. Is there a significant variation in the pressure built up in a 7.62 NATO case and a .308 Winchester case? The answer is both yes and no.
Fired rounds of ammunition produce different pressures, about 12,000 PSI on average, though, in practice, the difference can be up to 4,000 PSI. Even this tiny variation can severely affect anyone using a 7.62 or homemade shells in their gun.
Walls of brass
Despite having almost identical external dimensions, the 7.62 NATO casings have thicker walls than the .308 Winchester brass. The 7.62×51 brass has less space for powder than the .308 Winchester case, even though the difference may feel minimal.
Even though using calipers to measure the walls of fired brass might not give you definite answers, the scale won’t give you false information. The weight of .308 cases is generally around 160-170 grains, while 7.62 cases usually weigh over 180. (Yes, grains are an actual measurement of weight.)
Most cartridge casings are made of brass because brass is elastic and plastic. Elasticity describes a material’s ability to change shape in response to an applied force and return to its original form once removed. Plasticity describes a material’s ability to flow or deform permanently under the action of a force.
While this may sound contradictory, it isn’t. The high temperatures and expanding gases inside the casing cause it to grow and smash against the chamber walls. Due to the extreme chemistry inside, this reaction prevents the case from turning into a mini fragmentation grenade. This creates a barrier that does not allow exhaust gases to escape the firearm except through the barrel. Once the gases escape, the casing shrinks. It does not entirely return to its original shape and size. This all happens in just a fraction of a second.
Now let’s talk about recoil.
The recoil a shooter feels will depend on the person and the rifle. However, the amount of energy the recoil has is still a helpful way to compare different types of ammunition.
In this particular case, the 7.62x54R has a reputation for fierce recoil. Still, it only has about 10% more free recoil energy than the .308 Winchester. It makes sense that the 7.62x54R load uses more powder than the .308 Winchester load because they shoot the same weight bullet at the same velocity. Still, the .308 Winchester load is fired from a heavier rifle. Combining those factors produces less recoil energy for the .308 than the 7.62x54R.
Although the 7.62x54R cartridge doesn’t have a light recoil, other factors impact felt recoil. The 7.62x54R’s reputation is likely due to a poorly designed stock and a narrow metal butt plate on the typical Mosin-Nagant rifle.
Installing thicker and larger aftermarket recoil pads can reduce the felt recoil of a Mosin-Nagant rifle. The Mosin-Nagant has a higher weight, which helps with recoil reduction. A lighter weapon like the M38 or M44 Nagant Carbine will likely have more recoil than a heavier rifle. Put, a gun with a heavier bullet will generate more recoil than one with a lighter bullet.
The 7.62x39mm pack less than half the free recoil energy than the 7.62x54R and the .308 Winchester. This cartridge was designed to be easy to use and powerful enough for short to moderate-range work.
Even though it’s not as powerful as some of the more modern cartridges, the 7.62x54R is still a powerful cartridge that shoots relatively flat. This is especially impressive, given how old it is. The recoil of this gun is heavy, but it is about the same as a .30-06 Springfield.
The 7.62 NATO and .308 Winchester cartridges have impacted firearms history among military and civilians alike. In 1957, NATO officially adopted the 7.62 NATO round, which American forces and other NATO states have since employed. The .308 Winchester, commercially released in 1952 by Winchester, is a widely used cartridge for hunting and target shooting. While the 7.62 NATO and .308 Winchester cartridges look similar, there are subtle differences in pressure capacity, case sizing, and chamber dimensions. It is important for shooters to be aware of these differences and to ensure that they are using the correct cartridge for their intended purpose.
It should not be overlooked that the 7.62 NATO and .308 Winchester cartridges are not the singular ones designated as 7.62. There is also the 7.62x39mm, initially developed for the AK-47, and the 7.62x54R, a prevalent Russian sniper cartridge with varying attributes and capabilities. Knowing the discrepancies between these cartridges is vital for any shooter striving to sharpen their expertise and competencies. Considering everything, the 7.62 NATO and .308 Winchester ammo have remained dependable and potent offerings that have endured time’s test and may persist in being favored by shooters for many years.
Captain Hunter is a seasoned hunting mentor with over 20 years of experience in the field. His passion began as a young man on trips with his father and grandfather in the Colorado mountains. Today, he shares his unmatched skills in survival, tracking, and marksmanship through his website CaptainHunter.com. When he's not volunteering with youth hunting programs, you can find Captain Hunter providing expert hunting tips, gear reviews, and answers to your most pressing questions. His decades of experience make him the trusted guide to help any outdoorsman master the sport.