7.62x39 vs 7.62x51

So, you’ve been bitten by the 7.62 bug but don’t know whether the 7.62x39 or the 7.62x51 is right for you? Although both contain 7.62 in their name, the 7.62x39 and the 7.62x51 are very different cartridges with very different capabilities. In this article, I will cover these differences to help make your decision a bit easier.

Physical Attributes

Stood beside each other, you will see just how much of a difference exists between these 7.62s. In fact, the 7.62x51 stands at a maximum overall height of 2.800 inches compared to the 7.62x39’s relatively measly maximum overall height of 2.205 inches. This translates to an increase in length of just over 27% longer. Not only is the 7.62x51 longer, but it’s also wider as well. Looking at the base of each case, we find that the 7.62x51 has a 0.473-inch rim diameter, compared to the 0.447-inch rim diameter of the 7.62x39. This further solidifies the point that these cartridges are not interchangeable in any fashion.

Although these cartridges do not share any case dimensions, the naming leads one to believe they use the same bore size. As confusing as it may be, these cartridges do not typically use the same diameter bullets. In fact, the 7.62x51 utilizes 0.308-inch diameter bullets compared to the 0.310 to 0.311-inch diameter bullets most often loaded in the 7.62x39 (they can differ from this range, though these are typical). Larger diameters typically result in heavier bullet weights, but this is not the case with the 7.62x39. In general, the 7.62x39 is loaded with bullets ranging from 120-125 grains compared to the 145-175-grain range most often found with the 7.62x51. Bullet weights can exceed these ranges for each cartridge, though they are typically subsonic (at least with factory loads).

Power

Judging by the large difference in size between these cartridges, you probably already guessed that the 7.62x51 is more powerful than the 7.62x39. While there’s no denying this, it’s still important to realize the capabilities of each cartridge.

Looking at the Winchester 7.62x39 123-grain FMJ White Box specifications, we see that it produces 1,527 ft/lbs. of energy at a muzzle velocity of 2,365 feet per second. By comparison, the Winchester 7.62x51 149-grain FMJ White Box cartridge produces 2,575 ft/lbs. of energy at a muzzle velocity of 2,790 feet per second.

Based on these figures, the 7.62x51 produces nearly 69% more energy, only going 18% faster than the 7.62x39. It should also be noted that the 149-grain FMJ is much more aerodynamic than the 123-grain FMJ, which translates to 7.62x51 being superior for longer-range shots and more retained energy down range.

Plugging the figures from the loads referenced above into a ballistic calculator (149-grain FMJ: G1 ballistic coefficient of 0.456 vs 123-grain FMJ: G1 ballistic coefficient of 0.245), we see just how extreme the difference is. The 7.62x39 only reaches 470 yards before dropping to subsonic velocities (approximately 1,135 feet per second at sea level).

By comparison, the 7.62x51 remains supersonic out to 1,100 yards, still producing 425 ft/lbs. of energy. This is an increase of 2.34 times the supersonic range of the 7.62x39, which is substantial. In addition to velocity, the 7.62x51 also retains more energy.

Looking at the data, we see that the 7.62x51 produces as much energy at 340 yards, as the 7.62x39 does at the muzzle. Perhaps an even more stunning reference, is that the 7.62x51 retains more energy at 1,300 yards than the 7.62x39 at 500 yards (340 ft/lbs. vs 328 ft/lbs. respectively).

7.62x39 vs 7.62x51 Trajectory Comparison Using Hornady Ballistic Calculator (100-yard zero)

So, whether you’re after flatter trajectories, energy, or velocity, the 7.62x51 is the clear choice if you’re looking for performance.

Why 7.62x39?

With all the shortcomings of the 7.62x39, you’re probably wondering why anyone would choose it over the 7.62x51. Although the 7.62x39 loses to the 7.62x51 in nearly every respect, it is a much smaller cartridge overall. With this reduced size comes the distinct advantage of reduced weight, or more cartridges for the same weight, though this may not be a huge benefit to everyone.

Perhaps the main reason anyone chooses the 7.62x39 is that ammo is extremely affordable. At least, it used to be. While the 7.62x39 can still be had for about half the cost of 7.62x51 offerings (in some cases), it used to be a fraction of the cost in many cases just a few years ago. There are many reasons for the increase in cost, but perhaps the largest is the ban on the importation of most foreign-manufactured ammo.

Although these imports did not feature a brass case like many of the 7.62x39 offerings currently do, the steel-cased rounds were very cheap to produce. This translated to cheaper prices on the shelves, which was the primary appeal of the cartridge to many consumers. While there is no arguing that brass-cased offerings are of superior quality in almost every instance, the cartridge starts to lose much of its appeal as prices increase.

Perhaps the next largest reason anyone chooses the 7.62x39 is the AK platform. If you’re planning to get an AK platform of any type, but especially an AK-47 variant, it would be hard to pass up the cartridge it was designed for. For those who don’t necessarily care for the AK platform, however, the question you must answer is whether the cost savings of the 7.62x39 offset the far better ballistics of the 7.62x51.

Which 7.62?

For 7.62 cartridges, the 7.62x39 and the 7.62x51 are two of the most popular choices currently available. Though this may be the case, they are very different cartridges with very different capabilities, so you’re probably wondering which one is right for you.

For the AK platform, the 7.62x39 makes a lot of sense as it is the original chambering. When compared to the 7.62x51, the 7.62x39 is still cheaper to shoot which could be very beneficial for those who just wish to shoot as many rounds at the range as possible.

While the 7.62x51 is more expensive to shoot than the 7.62x39, its performance far exceeds the current difference in price. Whether you’re looking for power, trajectory, or velocity, the 7.62x51 is superior in every metric.

Regardless of which cartridge you choose, hopefully, this article helps make your decision a little easier.

--Banana Ballistics