300 Blackout vs. 5.56: A Complete Comparison

Designed in 2010 by Advanced Armament Corporation in cooperation with Remington and the US Special Operations Command, .300 Blackout has seen an explosion in popularity in recent years, promising shooters a compact, hard-hitting cartridge ideal for suppressed shooting, SBRs, and AR pistols. Since its inception, the cartridge has been called everything from a flash in the pan to a replacement for 5.56 NATO. But how do they actually stack up? We’re going to take an in-depth look at the history of these two cartridges, their ballistic performance, and their applications to see if of them comes out on top.

Brief Histories

5.56x45mm NATO

As World War II drew to a close, the lessons taught by the bitter, close-quarters combat of battles such as Stalingrad and Peleliu led many nations to begin exploring options for intermediate cartridges that would allow soldiers to carry more ammunition, had a battlesight zero more suitable for shorter engagement distances, and had lower recoil to facilitate automatic fire and more lightweight firearm designs.

Alongside the use of submachine guns, some early attempts to develop an intermediate cartridge even saw limited use during the war, including .30 Carbine, 7.92x39mm Kurz, and 7.62x39mm.

The British, in tandem with Belgian firearms manufacturer Fabrique Nationale, were also in the process of developing a .280 cartridge to replace the .303 British, but in 1954 the 7.62x51mm cartridge was selected as the first standardized cartridge for NATO use. While the British warned that this new cartridge would be too powerful for select-fire firearms, the US was unwilling to compromise on a reduction in power, and other NATO allies felt that standardization outweighed any potential concerns about ballistic performance.

Despite insistence on a more powerful round, the US began their own testing of small-caliber, high-velocity cartridges in 1957. The US Continental Army Command (CONARC) invited a number of firearms manufacturers and engineers, including Remington Arms, Springfield Armory, and Fairchild Industries (and their division, Armalite) to develop a new lightweight .22 caliber combat rifle with a number of specific parameters: it needed to fire a round that could remain supersonic at 500 yards, penetrate a steel helmet at that same distance, retain accuracy and ballistics equivalent to .30-06 M2 ball ammunition at 500 yards, and provide terminal ballistics that matched or exceeded the capabilities of the M1 carbine – all in a package that weighed under 6 pounds and had a magazine capacity of 20 rounds.

It was a tall order, and the first attempt to meet CONARC’s demands led Eugene Stoner of Armalite to produce a scaled-down version of the 7.62 AR-10 design, which would fire 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. As a result, Stoner reached out to Winchester and Remington with a request to increase case capacity, and Remington responded by developing in the .222 Special. Because there was already a commercially available .222 Remington cartridge, as well as several others under development for the CONARC project, .222 Special was renamed to .223 Remington, which readers will likely recognize as the civilian version of 5.56x45mm NATO.

Even still, the new AR-15 and its .223 cartridge weren’t immediately adopted – in 1959, Air Force General Curtis LeMay made a small order of them to replace M2 carbines in service after test firing the AR-15 for himself, and by the end of that year the rifle was approved for Air Force Trials.

LeMay ordered another 80,000 rifles in 1961, after rifle qualifications testing that pitted the AR-15 against the M-14 resulted in almost twice as many shooters achieving expert marksman scores with the AR-15. This was followed by Remington submitting the .223 cartridge to SAAMI, and after further operational testing, the cartridge was officially accepted by the US military under the Ball M193 designation. After a series of back-and-forth changes in the rifle’s design, a final contract was drafted for its production in 1964, and the M16 rifle was officially entered into service.

In 1970, NATO finally moved to select a new intermediate cartridge that would replace 7.62x51mm. Several options were submitted, but Fabrique Nationale eventually selected .223 Remington as the basis for the new standardized cartridge – and thus, 5.56x45mm NATO was born, and the rest, as they say, is history.

.300 BLK

The history of .300 Blackout is not as long or as winding as 5.56x45mm NATO, but it’s no less interesting. Though 5.56 had proven itself multiple times over as an effective combat cartridge, there were still some situations where its performance could be improved upon. Most notably, there was a strong demand from special operations units who conducted CQB missions for a cartridge that could outperform submachine guns chambered in 9mm Parabellum when shooting with short barrels and suppressors, without sacrificing the performance of a faster, more powerful rifle round.

This was a problem that manufacturers had attempted to solve before: in the 1960s, the US Air Force Armament Lab had experimented with a 7.62x28mm cartridge, but found it unreliable. Likewise, Colt had attempted to chamber AR-pattern rifles in 7.62x39mm, but the case angle of that cartridge caused issues with feeding even after modified AK-47 magazines were used. And while new cartridges such as 6.8 SPC and 6.5 Grendel did away with the need for proprietary magazines and demonstrated strong performance at shorter ranges, there were still issues with parts compatibility.

When Advanced Armament Corporation (AAC) was approached about the possibility of firing .30 caliber bullets from the M4 rifle platform without the need to swap out bolts, use specialized magazines, or sacrifice magazine capacity, they found inspiration by turning to the .300 Whisper cartridge developed by J.D. Jones in the early 1990s. That cartridge was itself 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.

Because .300 Whisper is a CIP standard cartridge, it couldn’t be submitted directly for US military use, as Remington follows SAAMI standards instead. As such, AAC used .300 Whisper as a blueprint, determined final specs for military use, and submitted the results to SAAMI, naming their cartridge the .300 AAC Blackout.

Case Dimensions and Common Grain Weights

One of the big draws of .300 BLK is that it only takes a barrel swap in order to use it in an AR chambered in .223 / 5.56, and since it uses a .223 case that has been cut down to accept a .30 caliber bullet, it’s probably no surprise that the case dimensions are similar. Base diameter, rim diameter, and overall length are identical between the two cartridges (0.376", 0.378", and 2.26" respectively), though .300 BLK has a substantially shorter case length (1.368" vs. 1.760”) and a wider neck diameter (0.334" vs 0.253”).

In fact, these similarities actually 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, causing 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 and .223 / 5.56 – many shooters use labeled magazines or different magazine styles to help differentiate, while others go as far as having a dedicated upper for each cartridge instead of simply swapping out barrels.

When it comes to grain weights, the first thing you’ll notice is how much heavier .300 BLK 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 NATO bullets. Both cartridges have a wide variety of specialized ammunition to choose from, whether you’re interested in competitive shooting, hunting, self defense, or just plinking at the range. But before we get into that, let’s do a brief ballistic comparison.

Ballistics

Before we get into the different applications for these cartridges, let’s take a look at how they stack up in terms of ballistic performance. For the purpose of this comparison, we’re going to be looking at 5.56 NATO fired out of a 16-inch barrel and .300 BLK fired out of a 10-inch barrel to simulate the most common configurations each cartridge was designed for.

As you can immediately see, the biggest outlier is the heavier .300 BLK subsonic round, which isn’t a surprise. These rounds were designed to be shot suppressed out of an SBR-length barrel in close quarters engagements, where performance beyond 150 yards is understandably an afterthought.

When we look at supersonic rounds, the ballistic performance is actually quite similar inside of 225 yards. 5.56 NATO shoots flatter and experiences less drop at longer ranges thanks to its superior velocity, but .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 actually 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 maintains an advantage of roughly 100 ft-lbs of bullet energy over 5.56 NATO at any given distance, but it’s when you look at short barrel lengths that .300 BLK’s advantage becomes even more stark. This is largely because .300 BLK achieves full powder burn out of a 9-inch barrel, while 5.56 requires a 20-inch barrel to reach its ballistic peak. 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 just under the speed of sound will achieve a bullet energy of only 135 ft. lbf.. But a 220-grain .300 BLK bullet traveling at the same speed will deliver a whopping 539 ft.lbf.

All in all, it comes down to what you want of your cartridge - .300 Blackout’s higher sectional density, superior barrier penetration, and larger wound channel give it a distinct edge in terms of terminal ballistics, while 5.56 NATO’s higher velocity and flatter trajectory make it a better choice for most shooters who are taking shots further than 250 yards.

Which is Better for Different Applications?

General Use / Plinking

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

Self Defense

When it comes to choosing one of these cartridges for self defense, there are several factors to consider. .300 BLK was designed for suppressors and shorter barrels, both of which are ideal for using indoors or out of a vehicle, but 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 that ensure rapid expansion while minimizing risk that a stray round will put others at risk. If you can afford the ideal setup, .300 BLK is certainly hard to beat when it comes to stopping a threat in close quarters.

Still, 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 both have no problem punching through multiple layers of drywall, tailor-made defensive 5.56 NATO ammo is both cheaper and more available than defensive .300 offerings, and are more likely to fragment on impact.

Hunting

Both .300 BLK and 5.56 NATO are excellent hunting cartridges, but the choice will ultimately come down to where and what you’re hunting. For small game and varmints inside of 200 yards, 5.56 is hard to beat, and there is a seemingly endless variety of frangible ammo available that will put down small game without passing through the animal or ruining the pelt.

But if you’re after larger game, 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. Blackout is also a great choice if you often hunt 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 that you really only want to use it for hunting inside of 150 yards to ensure an ethical kill – the slower velocity and faster bullet drop simply make shot placement too iffy at longer distances

SHTF

In a hypothetical SHTF situation, both cartridges would be more than capable of dealing with threats and putting meat on the table. 5.56 NATO does have a couple of obvious points in its favor – an AR-15 chambered in 5.56 is the most common rifle in the country, not to mention it’s government standard, which means there is a whole lot of ammo floating around. It’s also cheaper to stock up on and train with in advance, and the longer effective range could very well end up being a factor.

On the other hand, .300 BLK has a few perks, as well. In a suppressed, SBR package, you would have a highly maneuverable rifle that is about as close to “Hollywood quiet” as you’re going to get, and being able to reliably harvest larger game would certainly be welcome. The ability to defeat common barriers such as IIIA soft plate and automotive glass (and even bulletproof glass, thanks to the aerodynamic profile of the bullet) is also worth mentioning, and part of why .300 BLK appealed to military and law enforcement in the first place.

While 5.56 NATO probably gets the edge thanks to its widespread availability, it’s worth remembering that .300 BLK is only a barrel swap away – and as the saying goes, when it comes to 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. While subsonic 5.56 NATO ammo is technically available, there are simply too many reliability issues to make it a viable choice, and in many cases you’re left with what is essentially a straight-pull bolt action rifle as the AR fails to cycle properly.

Shooting supersonic ammo through a suppressor is certainly still quieter than shooting unsuppressed, and is especially useful for eliminating muzzle flash at night, but if you want a genuinely quiet rifle that functions without issue, reach for the .300 BLK. Ballistic performance is excellent inside of 150 yards even with the heaviest of subsonic rounds, and there is no need to worry about an over-gassed rifle or increased bolt carrier velocity. It’s what the cartridge was designed for, and it does the job admirably.

Final Thoughts

5.56 NATO and .300 BLK are both incredibly effective and versatile cartridges that excel in different areas, and making the choice between them will ultimately depend on your specific needs as a shooter. But unlike many other cartridge comparisons, this is one instance where you can have your cake and eat it, too, since buying a barrel is all that’s required to have access to both calibers – just don’t be surprised if you enjoy them both so much that you end up building another dedicated upper.