The 300 AAC Blackout and 7.62x39mm Soviet are two centerfire rifle cartridges that are extremely similar in terms of external ballistics and terminal performance.

The 7.62x39 has been a mainstay for former Communist Bloc countries for decades and has proven its combat effectiveness on the battlefield time and time again. However, integrating the 7.62x39 into the American AR platform has been fraught with difficulties as the cartridge design does not function well with AR-15 magazine design.

Despite these difficulties, shooters yearned for an intermediate 30-caliber cartridge in their AR-15's that could bridge the gap between the 5.56 NATO and 308 Winchester.

300 Blackout ammo is that bridge. There's no denying that the 300 Blackout closely mimics the 7.62x39, but there are differences between these two cartridges that makes some shooters question which cartridge is right for their next sporting rifle.

In this article, we will compare and contrast the 300 BLK vs 7.62x39 to help you understand the subtle nuances that make each cartridge unique and perfect for your next rifle.

What is the Difference Between 7.62 x39 and 300 Blackout?

The ballistic performance of 7.62x39 and 300 Blackout is almost identical. However, the difference between 7.62x39 and 300 Blackout ammo is that the 7.62x39 was developed during WWII for use in the SKS and AK-47, while 300 Blackout was developed in 2010 for use in a short barreled and suppressed M4 carbine. Furthermore, the 300 Blackout can fire supersonic and subsonic loads while most 7.62x39 ammo will be loaded for supersonic flight.

Is 7.62 x39 the Same as 300 Blackout?

No! The two cartridges are completely different and are not interchangeable.

You should never fire a round that your rifle is not chambered for, as doing so can cause a catastrophic failure that could damage your firearm and yourself.

Furthermore, although both rifle cartridges are labeled as 30-caliber, the 7.62x39 fires a 0.311" diameter bullet while 300 Blackout fires a .308" diameter bullet.

Cartridge Specs



When comparing two rifle cartridges, it's a good idea to analyze the cartridge specs to gain more knowledge of each.

One major difference between 7.62x39 and 300 Blackout is their case length, with the 7.62 being the longer of the two. This in turn affects the case capacity of both rounds, with the 7.62 having a higher case capacity of 35.6 gr H2O vs 26.5 gr H20 for 300 BLK.

Many would think that with almost 25% higher case capacity, the 7.62x39 will have a significantly higher muzzle velocity, but that's not actually the case. For 300 BLK supersonic loads using a 125 grain bullet there is only about a 100 fps difference between it and 7.62.

This is a true testament to the advancements in gunpowder technology since the development of the 7.62x39. However, using those advanced propellants comes at the cost of added pressure.

This is why the 300 BLK is rated for 55,000 psi vs 45,010 psi for 7.62x39 based on SAAMI specs.

Why Does 7.62x39 and 300 AAC Blackout Fire Different Bullet Diameters?

One interesting thing to note is that the 7.62x39 is not a true 30-caliber bullet based on the US standards of caliber measurement. The 300 BLK fires a 0.308" diameter bullet just like the 308 Winchester (7.62x51mm NATO), 30-06 Springfield, and 300 Win Mag. However, the 7.62x39 fires a 0.311" diameter bullet.

But why then is the Russian ammo designated a 7.62mm caliber? This is due to a discrepancy between how Russian and American gunsmiths measure bullet caliber.

In the photo to the right, you'll see an artistic depiction of barrel rifling. The high points are called "lands" while the low points are called "grooves."

Western gunsmiths use groove measurements to define the caliber of a bullet (which will be larger than land measurements). Even though the land measurement will be 7.62mm or 0.3" the actual bullet diameter will be 0.308" or 7.82mm because a bullet must contact the grooves of the barrel to for a tight seal.

To make things more confusing, Russian gunsmiths use land measurements to define bullet diameter. This means that the land measurement on an AK-47 or SKS, and therefore the true bullet diameter, will measure 0.311" or 7.90mm.

Recoil

Both the 300 Blackout and 7.62x39mm are well known for having mild recoil. Most shooters will not have a problem shooting either of them all day at the range.

As the 300 BLK has lower case capacity, it will generally have less recoil than the Russian 7.62x39.

On average over several supersonic loadings, the 300 Blackout will have 6 ft-lbs of felt recoil while the 7.62 will have 8.5 foot-pounds of recoil energy on average.

Most shooters will not have any issue handling the recoil from either rifle cartridge, as both are very mild, but for recoil sensitive marksmen the 300 BLK will be the better choice.

Trajectory

Trajectory is how we quantify a bullet's flight path as it travels downrange measured in inches of bullet drop.

Obviously, a flatter shooting cartridge is preferred for shooting longer ranges, as a shooter will require fewer adjustments to their optics to compensate for bullet drop. Having a flatter trajectory also means that a cartridge will be more forgiving of ranging mistakes.

Neither the 7.62 Soviet nor 300 Blackout round is known for having an extremely flat trajectory. However, the 7.62x39 will have the better trajectory of the two.

At 400 yards, the 123 grain 7.62x39 will have experienced about -44" of bullet drop while the 125 grain 300 BLK will have dropped approximately -68."

This trajectory of both 30-caliber intermediate cartridges limits their effective range to around 400 yards, which is exactly what they are designed for.

Subsonic 300 Blackout ammo makes the 7.62x39 look like it has the trajectory of a 308 Winchester!

At only 300 yards, 220 grain 300 BLK rounds have experienced around -100" of bullet drop. Again, this trajectory is not surprising, as subsonic loads are designed for close quarters combat, not long range shooting.

Ballistic Coefficient

Ballistic coefficient (BC) is a measure of how well a bullet resists wind drift and air resistance. Put another way, it's a numeric representation of how aerodynamic a bullet is. A high BC is preferred as this means the bullet will buck the wind easier.

Generally, heavy bullets will have a higher BC as it takes more force to disrupt the flight of a heavier bullet than a lighter one. Ballistic coefficient varies from bullet to bullet based on design, weight, and other factors that are beyond the scope of this article.

The 7.62x39 has an average BC of 0.27. Some of the heavier subsonic bullets for 300 Blackout have extremely high BC, such as the 208 gr Hornady 300 Blackout ammo (A-Max), at 0.648. However, 300 BLK ammo has a BC around 0.35 in general.

Although the two rounds have similar bullet weights (123 vs 125 gr), the 300 BLK is typically loaded with modern bullets that are more aerodynamic than the older design 7.62x39 projectiles.

Sectional Density

Sectional Density (SD) is the measure of how well a bullet penetrates a target. This is extremely important when hunting big and medium sized game, as you need a bullet that can punch through thick hide, bone, and sinew.

Sectional density is calculated by comparing the bullet weight and the bullet diameter. The higher the SD the deeper the bullet will penetrate into the target. This is a simplified view of penetration as there are other factors to consider, such as bullet expansion and velocity.

Bullet jacket design also plays a part in penetration, as a bullet designed to expand like a soft point (SP), ballistic tip, or jacketed hollow point (JHP) will naturally penetrate less than a full metal jacket (FMJ).

Average SD for 300 BLK comes out to 0.21 while the 7.62x39 measures at 0.18. These values are virtually the same and it is unlikely that any hunter or game animal will be able to tell the difference in penetration between the two rounds.

Hunting



Although neither round was designed with hunting in mind, hunters have found that both the 300 Blackout and 7.62x39 to be extremely effective on medium sized game at short range.

It is generally accepted that it takes 1,000 ft-lbs of energy to ethically harvest a whitetail deer. According to the Ballistics Tables below, this means that both rounds are effective against deer and ranges slightly below 200 yards.

Feral hog hunters enjoy the capabilities of the AR-15 platform and AK variants for engaging large herds of hogs that can decimate an entire field overnight. The semi-automatic capability of both rifles lends itself to quick follow-up shots that are extremely useful when trying to dispatch multiple hogs before the herd scatters.

A quick note on subsonic ammunition and hunting – it is NOT recommended to use subsonic loads for hunting medium game. The subsonic rounds simply do not have the terminal ballistics at hunting ranges to be effective and ethical at harvesting game. Therefore, make sure you are using supersonic .300 Blackout ammo when hunting.

Don't forget to stock up on your ammo. Visit our Fiocchi 300 Blackout ammo page for more affordable options.

Home Defense

There's no denying that the 7.62x39 Soviet is an extremely effective cartridge at both short and medium engagement distances. However, when it comes to home defense, the subsonic 300 Blackout cartridge is the superior choice for one reason:

Over Penetration

The 7.62 round is well known for its ability to penetrate barriers, and though this might be beneficial in wartime, it is a huge liability when it comes to home defense.

The last thing anyone wants in a self-defense situation is to injure an innocent bystander. As you are responsible for every bullet you fire, you do not want them ending up anywhere other than inside the bad guy.

In a home defense situation, it is very likely that you'll have neighbors nearby unless you live in the country. As such, the 7.62's ability to plow through barriers increases the risk of injuring an innocent bystander.

Since the subsonic loads were designed for close quarters battle (CQB) and to not over penetrate, this makes them the ideal choice for hone defense.

Combined with a suppressor, these rounds are completely hearing safe (no ear protection needed), which is a huge boon as shots fired inside a residence are usually louder since the sound echoes off the walls.

An AR pistol or rifle with a suppressor and a full mag of subsonic 300 Blackout ammo will be more than enough to handle any home defense situation.

The 7.62x39 is an extremely capable cartridge and will not have any problem repelling any would-be home invader, however the potential for over penetration with 7.62 makes subsonic 300 BLK ammo a better option.

Continue reading about the differences between 7.62x39 vs 300 Blackout ammo here.