Stood side by side, it is easy to see just how different the 223/5.56 and the 300 Blackout are in terms of appearance. Perhaps the biggest difference between the 223/5.56 and the 300 Blackout is the bullets they are using. The 5.56/223 uses 22 caliber projectiles, or 0.224” diameter, which generally range from 35 grains up to 95 grains (too heavy for most magazines). Factory loaded 223/5.56 ammunition generally ranges from 35 grains up to 77 grains to ensure that the ammo can fit in most magazines.
As its naming suggests, the 300 Blackout uses 30 caliber projectiles, or 0.308” diameter. This 0.084” increase in diameter over the 223/5.56 allows the 300 Blackout to fire much heavier projectiles ranging from 110 grains all the way up to and including 250 grains. Typical 300 Blackout factory load offerings range from 110 grains up to 220 grains.
Another major difference between the 223/5.56 and the 300 Blackout is the case length of each. The 223/5.56 has a nominal empty case length of 1.76 inches. Due to the long nature of heavy 30 caliber projectiles, the case of the 300 Blackout had to be shortened to 1.368 inches, or almost 0.4 inches shorter than the 223/5.56.
Although the empty case lengths of each cartridge may differ substantially, both cartridges have a maximum overall length of 2.26 inches when loaded (the max length that most AR-15 magazines will accommodate). With a similar overall height, you may have also noticed how similar the 223/5.56 and 300 Blackout cases look towards the base.
223/5.56 is one of the parent cases of the 300 Blackout, which means that they share the same base dimensions. Sharing the same base dimensions means that both cartridges can be used out of the same magazines (though the 300 Blackout typically operates more effectively in a 300 Blackout specific magazine). In fact, many reloaders use spent 223/5.56 cases to cut down and form 300 Blackout cases.
Power
Perhaps the biggest comparison made between the 223/5.56 and the 300 Blackout is the power that each cartridge can generate. Though they may not be generating a considerable amount of kinetic energy in terms of rifle cartridges, both the 300 Blackout and the 223/5.56 NATO have a SAAMI maximum pressure rating of 55,000 psi.
The most common 223/5.56 factory load offering is a 55 grain FMJ that produces around 1,281-foot pounds of kinetic energy at a muzzle velocity of 3,240 feet per second. A Hornady Frontier 300 Blackout, loaded with a 125-grain bullet produces 1,313 ft/lbs of kinetic energy at a muzzle velocity of 2,175 feet per second. Although the 300 Blackout is significantly slower than the 223/5.56, we can see that they are evenly matched in terms of muzzle energy…. At least with supersonic load offerings.
Subsonic ammunition is where these cartridges really differ. With a limited range of bullet weights (especially weights useful in the AR-15), the 223/5.56 is not very effective when it comes to subsonic ammo. In fact, the 223 Remington Atomic 77 grain HPBT subsonic offering is only producing 188 ft/lbs of kinetic energy at a muzzle velocity of 1,050 feet per second.
For reference, a 22 LR CCI Stinger is producing 191 ft/lbs of kinetic energy at a muzzle velocity of 1,640 feet per second. It should be noted that the 77-grain bullet has a much higher ballistic coefficient than the 32 grain 22 LR bullet; however, it is easy to see just how limited the 223/5.56 is when it comes to subsonic ammunition. (Keep in mind that depending on the firearm, subsonic 223/5.56 may not cycle reliably)
The 300 Blackout, on the other hand, has a distinct advantage when it comes to subsonic ammunition. With its much heavier range of 30 caliber projectiles, it is easy to guess why. Underwood’s 220 grain subsonic 300 Blackout offering produces 518 ft/lbs of kinetic energy at a muzzle velocity of 1,030 feet per second. This is nearly 3 times the amount of kinetic energy that the 223/5.56 subsonic offering is producing, meaning that the 300 Blackout is a superior choice for subsonic ammo.
Still, these 300 Blackout subsonic figures may not seem all that impressive when you consider that a 45 ACP can essentially duplicate them. Though this may be true, the long aerodynamic 30 caliber projectiles have a much better ballistic coefficient than the short and wide 45 caliber projectiles. This extends the useful range of the 300 Blackout over the 45 ACP, while also allowing it to retain more kinetic energy out to these further ranges. This does not, however, mean that subsonic 300 blackout loads are useful for long range shots by any means.
Barrel Length
When it comes to power, barrel length plays a key role in what each cartridge is capable of. Assuming both cartridges are fired from the same barrel length under 16 inches, the 300 Blackout will almost always be more efficient than the 223/5.56. What this means is that the 300 Blackout will not lose as much velocity (relative to the figures on the box) as the 223/5.56 will in these short barrel lengths.
In general, most 300 Blackout loads use pistol powders with a relatively fast burn rate. These powders, with their fast burn rates, do not usually require a long barrel to achieve a full burn. The 223/5.56 on the other hand, is primarily using rifle powders with a medium to slow burn rate. These powders take longer to achieve a full burn, which means that velocities can suffer in short barrel lengths.
Cost
When comparing the 223/5.56 to the 300 Blackout, it would be hard to avoid the topic of cost. In general, factory loaded 223/5.56 can be had for much cheaper than 300 Blackout ammunition. There are many reasons why this is, but the primary factors are the popularity of the 223/5.56 as well as its cheaper components.
The 223/5.56 is one of the most popular rifle cartridges currently available, both on the civilian market and with many Militaries around the world. Because of this, production levels are usually much higher for the 223/5.56 (especially military 5.56 NATO ammo) than the 300 Blackout. These increased production levels help to drive the price down considerably.
The other primary reason why 300 Blackout ammo is generally more expensive than the 223/5.56 is due to projectile cost. As previously discussed, 30 caliber projectiles are much heavier than 22 caliber projectiles. Increased weight leads to increased materials, which leads to increased production costs. Even with the increased savings of reloading, 300 Blackout is more expensive to reload than the 223/5.56 due to the extra cost of the 30 caliber projectiles.
Because of these factors, it is unlikely that 300 Blackout ammo will ever reach the same price as the cheapest 223/5.56 offerings. It should be noted, however, that many 300 Blackout offerings have dropped considerably in price over the years, especially supersonic offerings.
Final thoughts
The 223/5.56 and the 300 Blackout have become two of the most popular chamberings for the AR-15 platform. Though they are both very popular options, they offer very different capabilities. With these differences, it can be daunting trying to figure out which cartridge is right for you.
If you’re in search of exceptional velocities with the ability to effectively make hits out to longer ranges, the 223/5.56 is the clear winner. Paired with the fact that 223/5.56 ammo can most often be had much cheaper than the 300 Blackout, it is an easy choice for the wallet.
If, however, you don’t mind spending a little more on ammo with the intention of having the shortest and quietest firearm chambered in a rifle cartridge, the 300 Blackout is a hard option to beat. Although the 300 Blackout may not be known for its long-range capabilities, supersonic offerings can be very effective out to medium ranges.
Perhaps you like the unique capabilities of both cartridges but don’t want two separate AR-15s lying around. Because the 300 Blackout and the 223/5.56 use the same bolt, magazines, and receivers, it is very common to buy an AR-15 chambered in one of the cartridges and buy a separate upper chambered in the other cartridge. This not only saves money but also saves the headache of having to rearrange your whole safe to fit two complete AR-15s in it.
Regardless of which way you choose to go, hopefully this article made your decision a little easier.
–Banana Ballistics