300 Blackout vs. 5.56: A Complete Comparison

Designed in 2010 by the Advanced Armament Corporation (AAC) with Remington and the US Special Operations Command, the .300 Blackout has seen an explosion in popularity. Promising shooters a compact, hard-hitting cartridge ideal for suppressed shooting, SBRs, and AR pistols.  

Since its creation, people have called this cartridge many things. Some say it is a flash in the pan while others think it could replace the 5.56 NATO. But how do these two cartridges compare?   

Let's take an in-depth look at the history of the 556 vs 300 Blackout. We will discuss their ballistic performance and applications to see if one of them comes out on top.   

Brief Histories 

5.56x45mm NATO 

As World War II ended, many nations learned from the hard battles of Stalingrad and Peleliu seeking new options for intermediate cartridges. These 5.56 rifle cartridges allowed soldiers to carry more ammunition while providing zero battlesight for shorter distances. Additionally, they offered lower recoil facilitating automatic fire and development of lightweight firearm designs.  

In addition to using submachine guns, early efforts to develop an intermediate cartridge emerged during the war, though they saw limited use, these included:  

• .30 Carbine  
• 7.92x39mm Kurz 
• 7.62x39mm  

The British, in collaboration with the Belgian firearms manufacturer Fabrique Nationale, developed a .280 cartridge as a replacement for the .303 British.  

1954: NATO adopted the 7.62x51mm cartridge and was selected as the first standardized cartridge.  

The British warned that this new cartridge could be too powerful for certain firearms, however the United States was unwilling to compromise on reducing its power. Meanwhile, other NATO allies prioritized standardization over performance concerns.  

1957: Despite insistence on a powerful round, the U.S. began testing small-caliber and high-velocity cartridges.  

The US Continental Army Command (CONARC) invited several firearms manufacturers and engineers to develop a new lightweight .22 caliber combat rifle with specific parameters, including Remington Arms, Springfield Armory, and Fairchild Industries (and their division, Armalite). These specific parameters included:   

• The ability to fire a round that remained supersonic at 500 yards.   
• Penetration of a steel helmet at the same distance while maintaining accuracy and ballistics equal to .30-06 M2 ball ammunition. 
• Terminal ballistics that matched or exceeded capabilities of M1 carbine. 
• A total weight of 6 pounds and magazine capacity of 20 rounds.   

 
To meet CONARC's demands, Eugene Stoner of Armalite produced a scaled-down version of a 7.62 AR-10 design. One that fires a cartridge produced from a lengthened 222 Remington case and a custom powder load developed by Robert Hutton.   

Initial tests were encouraging, but the chamber pressures were too high. Stoner contacted Winchester and Remington to request an increased case capacity, and this resulted in the development of the .222 Special.  

Because there was already a commercially available .222 Remington cartridge, as well as several others under development for the CONARC project, the .222 Special, was renamed to .223 Remington, which you may recognize as the civilian version of 5.56x45mm.  

Even still, the new AR-15 and its .223 cartridge were not immediately adopted.   

1959: Air Force General Curtis LeMay replaced M2 carbines after test firing the AR-15 resulting in the approval of the rifle for the Air Force Trails.   

1961: LeMay ordered 80,000 rifles which were compared to the M-14, resulting in twice as many shooters scoring expert marksman with the AR-15. This was followed by Remington submitting the .223 cartridge to SAAMI (Sporting Arms and Ammunition Manufacturer’s Institute). After further operational testing, the US military officially accepted the cartridge under the Ball M193 designation.  

1964: A final contract was drafted for production after several modifications to the rifle's design, and the M16 rifle officially entered service.   

1970: NATO finally moved to select a new moderate cartridge that would replace 7.62x51mm. Several options were submitted, but the Fabrique Nationale selected the .223 Remington as the basis for the new standardized cartridge.   

This led to the 5.56x45mm NATO, and the rest, as they say, is history.  

.300 BLK 

The history of the .300 Blackout is not as long as the 5.56x45mm NATO, but it’s no less interesting. Although the 556 demonstrates its effectiveness as a combat cartridge there are situations that could have improved performance.

  
Special operations units conducting CQB missions required a cartridge that outperformed submachine guns chambered in 9mm Parabellum. They needed a firearm capable of effective use with short barrels and suppressors without sacrificing performance of a faster and powerful round, an issue manufacturer has attempted to solve since the 1960s.  

The US Air Force Armament Lab and Colt experimented with a 7.62x28mm cartridge but found it unreliable, as it experienced feeding issues due to the cartridge’s case angle when using modified AK-47 magazines.  

New cartridges like the 6.8 SPC and 6.5 Grendel removed the need for proprietary magazines demonstrating strong performance in shorter ranges yet faced issues with part compatibility.    

When Advanced Armament Corporation (AAC) was approached about the possibility of firing .30 caliber bullets from the M4 rifle platform without swapping bolts, specialized magazines, or magazine capacity, they found inspiration in the 300 Whisper cartridge developed by J.D. Jones in the early 1990s. That cartridge was originally based on a 221 Fireball case necked up to accommodate a .30 caliber bullet, though reloaders soon realized that a shortened and resized .223 case was just as effective.  

Since the .300 Whisper is a CIP standard cartridge. They couldn’t submit directly for U.S. military use, as Remington follows SAAMI standards. The AAC used 300 Whisper as a blueprint to determine the final specs for military use and submitted the results to SAAMI, naming their cartridge the 300 AAC Blackout.   

5.56 NATO vs. .300 Blackout Specifications Overview 

Case Dimensions and Common Grain Weights 

A key advantage of the 300 BLK vs 556 is it only requires a barrel swap to use an AR platform chambered in .223 / 5.56. Since the .223 case has been cut down to accept a .30 caliber bullet, there is no shock that the case dimensions are similar.   

However, these similarities create a potential safety hazard: because of similar case and chamber dimensions, 300 BLK cartridges with certain bullet lengths, seating depth, and powder charge can potentially be chambered in a .223 barrel despite being larger than the bore. This causes an extreme pressure spike when fired that will likely destroy the firearm and potentially injure the shooter.   

For this reason, it is extremely important to keep ammunition separate if you shoot both .300 BLK, 5.56 NATO and .223. Shooters should use labeled magazines or different magazine styles to help differentiate. If possible, have a dedicated upper for each cartridge instead of simply swapping out barrels.   

Regarding grain weights, the first thing you will notice is how much heavier .300 Blackout bullets are – ranging from 110 or 125 grain supersonic rounds to the subsonic 200 and 220 grain rounds, .300 BLK averages around 2-4x the grain weight of most 5.56x45mm bullets.  

Both cartridges offer a wide variety of specialized ammunition to choose from. Before we discuss that, let’s do a brief ballistic comparison. 

Ballistics 

Before discussing the different applications for these cartridges, let’s first look at their ballistic performance. For this comparison, we will look at 5.56 NATO fired from a 16-inch barrel vs. 300 Blackout fired from a 10-inch barrel, simulating the most common configurations each cartridge was specifically designed for.  

As you can immediately see, the 300 Blackout subsonic round is heavier. These rounds specifically designed for shooting suppressed out of short-barreled rifles (SBR) in close quarters engagements. Therefore, performance beyond 150 yards is understandably an afterthought.  

Looking at supersonic rounds, the ballistic performance is similar inside 225 yards. The 5.56 NATO shoots flatter and experiences less drop at longer ranges thanks to its superior velocity. However, the .300 BLK is still more than capable of making accurate shots out to 300 yards.   

Though it may not look like it, .300 BLK bullets have a higher ballistic coefficient but lack the velocity to take advantage of that fact.  

While 5.56 will certainly require less holdover at longer distances, .300 BLK still packs quite a wallop even at 500 yards, thanks to its significantly larger mass. Even out of a 16-inch barrel, .300 BLK has an advantage of roughly 100 ft-lbs of bullet energy over 5.56 NATO at any given distance.  

However, it’s when you look at short barrel lengths that 300 BLK’s advantage becomes even more stark. This is largely because the .300 Blackout burns all its powder in a 9-inch barrel, while the 5.56 needs a 20-inch barrel to reach its best performance.  

In fact, a 110-grain .300 BLK bullet fired out of a 10.5-inch barrel has slightly more muzzle energy than a 55-grain 5.56 bullet fired out of a 16-inch barrel!   

If that wasn’t enough to illustrate the point, we can also compare subsonic performance. A 55-grain 5.56 NATO round traveling under the speed of sound will achieve a bullet energy of 135 ft. lbf.. But a 220-grain 300 BLK bullet traveling at the same speed will deliver a whopping 539 ft.lbf.   

Ultimately, it all depends on what you want from the cartridge. The .300 Blackout has a higher sectional density. It also has superior barrier penetration, and larger wound channel that give it a unique advantage regarding terminal ballistics.  

While the 5.56 NATOs have a higher velocity and flatter trajectory. This makes it a better choice for shooters who are shooting further than 250 yards. 

Which is Better for Different Applications? 

General Use / Plinking 

If you’re punching holes in paper or running drills at the range, we recommend the 5.56 NATO. The benefits that 300 BLK have are unnecessary for plinking, and you can find bulk 5.56 ammo much cheaper. Both rounds exhibit similar performance at the distances you’re likely to be shooting at for fun, and switching to .300 BLK isn’t likely to have any impact on the muscle memory you’ve developed from practicing with 5.56.  

Self Defense 

To choose one of these cartridges for self-defense, there are several factors to consider, the .300 BLK, designed for suppressors and shorter barrels make it ideal for indoor use or out of a vehicle. However heavier subsonic rounds are also much more likely to over-penetrate.  

Thankfully, there are a number of supersonic defensive rounds available from manufacturers such as Fiocchi and Lehigh. These ensure rapid expansion while minimizing the risk that a stray round will put others at risk. If you can afford the ideal setup, 300 BLK is certainly hard to beat to stop a threat in close quarters.  

Yet not everyone is in a position to secure either one of the required tax stamps for a suppressed SBR, let alone both. If you’re shooting 300 BLK out of an unsuppressed mid-length barrel, there’s significantly less difference, and while 5.56 NATO and .300 BLK have no problem punching through multiple layers of drywall.  

The tailor-made defensive 556 ammo is both cheaper and more available than defensive .300 offerings and is more likely to fragment on impact. 

Hunting 

Both 300 Blackout and 5.56 are excellent hunting cartridges, but the choice will ultimately come down to where and what you’re hunting. For small games and varmints within 200 yards, we recommend the 5.56 as the best option. A variety of frangible ammo is available enough to take down small games for minimal penetration and injury.  
 
But if you’re after larger games, such as deer, hogs, or even smaller black bears, .300 BLK offers far superior terminal ballistics thanks to its larger mass and wider wound channels. The 300 Blackout is also a great choice for hunting in thick brush. Where the lower risk of deflection makes it more likely that your bullet will end up where you meant it to go.  

The caveat with 300 BLK is best for hunting within 150 yards. This ensures an ethical kill. The slower velocity and faster bullet drop make shot placement too iffy at longer distances.  

SHTF  

In a hypothetical SHTF situation, both cartridges can handle threats and putting meat on the table. The 556 has some clear advantages.  

A AR-15 platform chambered in AR 556 is the most common rifle in the country. It also meets government standards, meaning there is a whole lot of ammo floating around. Stocking up and training in advance is cheaper and the longer effective range could well end up being a factor.  
 
On the other hand, the 300 BLK also has a few advantages. In a suppressed, SBR package, you have a highly maneuverable rifle. As close as it gets to “Hollywood quiet”, and being able to reliably hunt larger game is a huge advantage.  

The ability to overcome common barriers is worth mentioning. This includes IIIA soft plate, automotive glass, and even bulletproof glass, thanks to the aerodynamic profile of the bullet. Which was also part of why the 300 BLK appealed to military and law enforcement in the first place.  

While 5.56 NATO gets the edge thanks to its widespread availability, it’s worth remembering that .300 BLK is only a barrel swap and as the saying goes, in terms of preparation, two is one, and one is none. 

Shooting Suppressed 

No need to mince words – if you’re interested in shooting suppressed, .300 BLK is the way to go. Although subsonic 5.56 ammo is technically available, there are many reliability issues to make it a viable choice. In many situations, you'll end up with a straight-pull bolt action rifle since the AR platform fails to properly cycle.  

Shooting supersonic ammo through a suppressor is much quieter than shooting without one. This is especially useful to eliminate muzzle flash at night. If you are looking for a genuinely quiet rifle that functions without issue, choose the 300 BLK.  

The ballistic performance is excellent within 150 yards. Even with the heaviest subsonic rounds, you don't need to worry about an over-gassed rifle. You also don't have to worry about an increased bolt carrier velocity. This cartridge serves this purpose, and it does the job admirably. 

Final Thoughts 

5.56 NATO and 300 BLK are both incredibly effective and versatile cartridges. They both excel in different areas. The choice between them ultimately depends on the specific needs of a shooter.   

Unlike other cartridge comparisons, this is the case where you can have your cake and eat it, too. Buying a barrel is the only requirement to have access to both of these calibers. Don’t be surprised if you enjoy them both so much that you end up building another dedicated upper.

  
Also, be sure to explore the Ultimate Guide to 300 Blackout [Ballistics, Comparisons, & More] for an in-depth look of the .300 Blackout.