300 Blackout vs 7.62x39

Banana Ballistics • October 24, 2023

If you have ever wanted to get into a heated argument about two calibers, the 7.62x39 and the 300 Blackout might be top contenders. Although they are very similar cartridges in some respects, the 7.62x39 and the 300 Blackout are very different cartridges overall, making for a tricky decision. In this article, we will be going over some similarities and differences of these cartridges to help make your decision a little easier.

Physical Attributes

Although the 7.62x39 and the 300 Blackout are both considered 30 caliber cartridges, the projectiles used by each differ slightly in diameter. Unlike the 300 Blackout, which is a true 30 caliber bore size (0.308 inch in diameter), the 7.62x39 has a slightly larger bore size, using bullets that are 0.310-0.311 inch in diameter. This diameter is far less common than 0.308-inch diameter bullets. However, there are several options for those who wish to reload the cartridge.

Image relating to 300 Blackout vs 7.62x39
7.62x39
Image relating to 300 Blackout vs 7.62x39
300 Blackout

Stood side by side, it is easy to see that the 7.62x39 case has a taller and wider stature than the 300 Blackout. In fact, an empty 300 Blackout case has a nominal length of 1.368 inches compared to the 7.62x39’s longer nominal case length of 1.524 inches. The 7.62x39 also has a wider rim diameter of 0.447 inches compared to the 300 Blackout’s rim diameter of 0.378 inches (same as 5.56/223 Rem).

With its additional height and width, the 7.62x39 has a much larger case capacity when compared to the 300 blackout. An empty 7.62x39 case has an H2O capacity of approximately* 35.6 grains, whereas an empty 300 Blackout case only has an H2O capacity of approximately* 26.5 grains. This difference equates to the 300 Blackout only having 74.4 percent the capacity of the 7.62x39.

Image relating to 300 Blackout vs 7.62x39
300 Blackout & 7.62x39

Power

Considering the large difference in case capacity, it would be easy to think that the 300 Blackout produces considerably less power than the 7.62x39. There is one factor, however, that we have not discussed, which is pressure. According to SAAMI, the 7.62x39 has a maximum pressure rating of 45,010 psi compared to the 300 Blackout’s much higher maximum pressure rating of 55,000 psi.

With its higher maximum pressure rating, the 300 blackout’s performance comes much closer to the 7.62x39 than the capacities would have you believe. Looking at Winchester USA’s 123 grain FMJ 7.62x39 load, we see that it is generating 1,527 ft/lbs. of kinetic energy at a muzzle velocity of 2,365 feet per second. Looking at Winchester USA’s 125 gr Open Tip 300 Blackout load, we see that it is producing 1,325 ft/lbs. of kinetic energy at a muzzle velocity of 2,185 feet per second.

Though these figures differ by over 200 ft/lbs., the 300 Blackout produces around 86.8 percent of the kinetic energy of the 7.62x39 at the muzzle. Considering the large difference in case capacity between these cartridges, this is an impressive feat.

Subsonic

When it comes to the power of subsonic ammunition, the 7.62x39 and the 300 blackout offer almost identical performance with the 7.62x39 having a slight edge due to heavier bullets. That is at least if you can find subsonic 7.62x39 ammunition.

In its most common configuration, the 7.62x39 is loaded with bullets ranging from 122-150 grains, which travel much faster than the speed of sound. In recent years, a few subsonic loadings have been introduced for the 7.62x39, such as the Hornady 255 gr SUB-X. It should be noted however, that these subsonic offerings can be very hard to acquire and are potentially unreliable.

Most 7.62x39 chambered firearms utilize barrels with a 1-9.5 (or very close) or 1-10 twist rate. Though these twist rates are optimal for stabilizing the 122-150 grain projectiles typically fired from this cartridge, they can lead to issues when stabilizing heavy, subsonic projectiles. Due to the combination of hard-to-find ammo and sub optimal twist rates, the 7.62x39 is not an ideal subsonic option.

The 300 Blackout on the other hand, is currently one of the most popular cartridges when it comes to subsonic offerings. In fact, most 300 Blackout chambered firearms utilize fast twist rates (1-7 or 1-8) and short gas systems with the intention of using heavy subsonic bullets (while being suitable for lighter supersonic offerings).

Along with the vast number of firearms set up to run subsonic ammunition comes a plethora of factory loaded subsonic offerings for the 300 Blackout. As its popularity increases, so does the number of subsonic offerings, making it ideal for those that wish to be as quiet as possible.

Cost

Let’s face it…. Almost none of us have an unlimited budget, so when it comes time to pick between cartridges, cost is often a giant factor (especially for rifles that are shot more than a couple times a year). While the 7.62x39 and the 300 Blackout aren’t necessarily expensive cartridges to shoot, there are several cost-related factors to consider before choosing one.  

If you wish to shoot as cheaply as possible, steel cased 7.62x39 is currently the most economical option. When it comes to centerfire rifle cartridges, steel cased 7.62x39 has long been one of the cheapest options on the market. Historically, this has been due to a massive amount of steel cased cartridges being imported from countries outside the United States.

Over the last several years, however, there have been many bans placed on the importation of munitions from many countries. Due to these bans as well as supply factors, steel cased 7.62x39 options have been dwindling and increasing in price, though it can still generally be found much cheaper than conventional 300 Blackout ammo.

If, however, steel cased ammo does not suit your fancy, the price of reloadable brass cased ammo tends to be very similar between these cartridges. In fact, many brass cased offerings of the same manufacturer and bullet style tend to be very similarly priced (if not the same) between the 300 Blackout and 7.62x39. With this in mind, cost may not be a primary deciding factor for those wanting to use only brass cased ammo.

Which One Should I Get

With the benefits and drawbacks of each cartridge, it can be a daunting task choosing between the 7.62x39 and the 300 Blackout. So, the question becomes, which one should I get?

If you’re looking for a moderately powerful 30 caliber cartridge with good short to mid-range ballistics, the 7.62x39 is an enticing option. With its various steel cased options (at least for now), the 7.62x39 is a great option for those on a budget.

If, however, you want to be as stealthy as possible while having the ability to use supersonic ammo when needed, there may not be a better option than the 300 Blackout. Though it might not be quite as powerful or economical as the 7.62x39, it does offer some major benefits that make it a great choice.

With the various benefits that each cartridge has over the other, it would be very hard to go wrong with the 7.62x39 or the 300 Blackout. Regardless of which caliber you choose, hopefully this article made your choice a little easier.

*The case capacities listed represent the approximate amount of H2O that will fit inside an empty case. These values can vary based on the manufacturer as different companies will typically result in slightly different case capacities.

--Banana Ballistics