300 Blackout vs 556: Differences and Uses

Selecting the proper caliber for your needs is necessary to get the most out of your firearm. This is especially true when dealing with AR-15 platforms. Over the years the AR platform has been modified to accept a multitude of different calibers.

However, most of those caliber changes require a significant number of modifications to the rifle itself, making them a complex and expensive decision. But this is not the case with .300 Blackout.

Using .300 Blackout in your AR-15 is one of the easiest caliber conversions to do, but it does raise some questions.

Questions like…

What are the benefits of .300 Blackout vs 5.56?

And what is the performance of 5.56 vs .300 Blackout?

To answer those questions we will have to look at and compare each of these rounds. This includes their intended use, dimensions, and performance

What Is 300 Blackout?

US Special Forces were interested in a new cartridge that would add to their capabilities while not complicating their supply chain. Additionally, there was a desire to meet or surpass the current ballistic performance of ammunition and weapon systems currently available to them.

There were three major parameters that needed to be met by the new cartridge. The first parameter was that it must exceed the subsonic performance of 9mm Luger. The second parameter was that the round perform equal to or better than 7.62×39 at supersonic speeds. Finally, the round must also be compatible with the M-16/M4 family of weapons with few modifications.

A 1990s era wildcat cartridge known as the .300 Whisper fit many of these criteria, but since it was not certified by the Sportings Arms and Ammunition Manufacturer’s Institute (SAAMI) it could not be formally adopted by the US military and put into inventory.

Between 2009 and 2010 the concept of the .300 Whisper was standardized by Advanced Armament in a way that it would work with standard M4 parts and magazines. The finished designs were submitted to SAAMI and approved in early 2011, resulting in the 300 BLK or 300 Blackout as we know it today.

The 300 Blackout was able to use the same bolts, lowers, magazines, and uppers as 5.56 NATO. The only difference was the caliber of the projectile which required a simple barrel swap to change between cartridges

This allowed for the use of an already developed and supported weapon system without the need of adopting a new firearm in addition to a new cartridge.

The round was intended to fulfill a close quarters’ role while providing better performance in both suppressed circumstances and shorter barreled rifles. Previously this role was filled by submachine guns like the integrally suppressed MP5SD. However, the ballistic performance of 9mm did not compare to rifle rounds.

This meant with the adoption of 300 Blackout, an M4 style rifle could be used with shorter barrel lengths and still be effective when compared with 5.56 rounds out of similar length barrels.

Let’s compare these rounds.

300 Blackout vs 556: The Ultimate Comparison

Since both of these rounds were designed to use the same or similar rifle type, we can expect to find them very similar in their dimensions. However, this does not always equate to similar ballistic performance.

Before we get into that, let’s look at these rounds’ design.

5.56 vs 300 Blackout Design

Both 5.56 and 300 Blackout are intermediate cartridges. This means they do not meet the power of a full-powered rifle round like .308 or 7.62×51 NATO but exceed the terminal performance of pistol rounds.

The 5.56 round was developed from the ground up to provide an effective but lighter round for infantry use. This meant that the individual soldier could carry more rounds on their person and in the gun with a similar weight to the equivalent combat load with 7.62×51 NATO. This also meant a lighter weapon which would result in better combat effectiveness and less fatigue in the field.

On top of this, since it was to be the primary round of the infantry it had to work at a variety of ranges. The standard 5.56 is still effective at roughly 500 yards (just under 500 meters) and can be pushed to 1000 yards depending on the conditions and shooter.

While 5.56 was made for more general purposes, 300 Blackout is better described as a special use round. It evolved from the need for close combat with suppressed weapons and night vision. This built a number of restrictions into the round from the beginning.

Its maximum range for expected use was roughly 300 yards. This is because of how it was going to be used by special forces and the limitations of night vision equipment.

Since we know the general design purpose of these rounds, let’s break them down.

.300 vs 5.56 Casing

There are numerous similarities in the case dimensions. This is to be expected when rounds can be easily used with roughly 90% of the same parts.

The 5.56 case is a rimless, tapered case that is bottlenecked down to accept a 5.7 mm diameter projectile.

The neck diameter is 6.43 mm while the shoulder diameter is 9 mm. The base diameter is 9.58 mm with a rim diameter of 9.6 mm and a rim thickness of 1.14 mm. The case itself is 44.7 mm long with the overall length with a seated projectile being 57.4 mm or 2.260 inches.

The 300 Blackout uses the base 5.56 case. This allows for 300 Blackout to be reloaded into previously used 5.56 cases. However since the 300 Blackout uses a .308 projectile, the neck and base diameters differ from the 5.56 case

The 300 Blackout’s neck diameter comes in at 8.46 mm with a shoulder diameter of 9.14 mm. The base diameter is 9.54 mm with a rim diameter of 9.6 mm and a rim thickness of 1.14. Since the case needs to be shortened to accommodate a similar overall length and a .30 caliber projectile the case length is 34.9 mm with an overall length of 57 mm.

Here is a table to easily compare the dimensions:

300 Blackout vs 5.56 Projectile Weight

While the case differences are roughly similar to each other, the projectile weights of 300 Blackout and 5.56 are drastically different.

Because of this, the performance of each round is different. The 5.56 round relies on its velocity and hypersonic speed to inflict damage. It requires comparatively lightweight projectiles with a small diameter.

This leads to some 5.56 projectiles weighing anywhere from 36 grains to 112 grains. However, the 112-grain projectiles are meant for subsonic use. The average projectile weight is between 40 grains and 77 grains in most loadings.

On the other hand, 300 Blackout relies on a combination of bullet weight and velocity to deal damage. This is because subsonic rounds require more weight to allow them to penetrate targets more easily. In the hypersonic forms of 300 Blackout, this weight aids in defeating barriers.

Projectiles for 300 Blackout range from as little as 78 grains to as heavy as 240 grains, with 220 grains being the average. This is generally almost twice the weight of its 5.56 counterparts. However, some of the heavier loads require faster twist rates to stabilize the projectile in flight.

556 vs 300 Blackout Performance

The performance of these two rounds comes down to application. Both are easily lethal with correct shot placement, range, and projectile choice.

The 5.56 round has a much longer effective range than the 300 Blackout. While 1000 yard shots are not out of the question, most uses of the round will be within 500 yards. It will penetrate a US steel helmet at 500 yards and still carry enough energy to be lethal as it was designed to do.

However, overpenetration is less of an issue with 5.56 projectiles. This comes down to overall design and how the projectile is designed to partially fragment and tumble once it impacts a solid object.

The light weight of the projectiles also contributes to its terminal performance while hampering its ability to go through denser materials. When used to try and defeat cover, 5.56 has to use more rounds compared to .30 caliber ammunition.

On the opposite end of the spectrum, we find 300 Blackout. Heavier overall, the .300 Blackout projectiles match or exceed the weight of 7.62×39 projectiles. This makes sense as 7.62×39 was the baseline performance expected from supersonic 300 Blackout.

These heavy bullets also help at subsonic speeds. This is because heavier bullets going slower are less likely to stop once they impact something than lighter bullets at similar velocities. Instead of relying on speed to carry them through the material, these projectiles rely on weight to make them harder to stop.

In regards to suppressed weapons, 300 Blackout is extremely useful. When suppressed it can work in shorter-than-normal barrel lengths, generally in the 8-10 inches range. Comparatively, 5.56 used in barrels under 10 inches begin to experience reliability issues.

This means 300 Blackout can be used in an overall shorter package while still delivering lethal results within Close Quarters Combat ranges

5.56 vs 300 Blackout Power and Range

The power and range of these rounds vary depending on barrel length, projectile weight, powder used, etc.

This makes it harder to compare the two rounds since they are designed to be used with different barrel lengths. The performance of a standard 5.56 round out of a 20-inch barrel is not necessarily a good comparison to 300 Blackout out of a barrel almost 10 inches shorter.

If we take a look at either round we can see that 5.56 is faster than the standard 300 Blackout round. However the foot-pounds they produce and retain differ over distance. The drop of the bullet inflight also differs depending on barrel length, with shorter barrels causing a significant difference in drop for 5.56 than when it is used in longer barrels.

Since most combat happens within 546 yards (500 meters) and most civilian encounters occur well within 40 feet we will compare these two rounds with the same barrel length at various ranges maxing out at 500 yards.

We’ll use a 9-inch barrel length as standard. While this heavily favors 300 Blackout it will clearly illustrate why it performs better in Close Quarters.

A 55 grain M193 5.56 projectile has a velocity of 2,591 feet-per-second (fps) at the barrel with 820 foot-pounds (ft-lbs) of energy. Comparatively, a 110 grain 300 Blackout projectile is moving at 2,116 fps with 1,094 ft-lbs of energy.

This is a significant difference in velocity and energy with the 5.56 having a higher velocity and the 300 Blackout having more energy. 

At half of our maximum distance, 250 yards, the 5.56 round will have a velocity of roughly 1,793 fps with 392 ft-lbs of energy. The 5.56 round has lost half of its overall energy but is still going faster than the 300 Blackout projectile.

The 300 Blackout round will be going at roughly 1,515 fps with 561 ft-lbs of energy. While going about 200 feet slower at 250 yards, the 300 Blackout has lost only a fourth of its speed and a little less than half of its total energy.

By 500 yards 5.56 will have roughly a velocity of 1,210 fps with 179 ft-lbs of energy and 300 Blackout will be going at about 1,111 fps with 302 ft-lbs of energy. This makes 300 Blackout a harder hitting round but it does not make it the perfect “do-it-all” caliber.

Recoil 5.56 vs .300 Blackout

Due to how these rounds behave, 300 Blackout has roughly three times the recoil of a 5.56 round. However, the felt recoil is not noticeably different. This increase in recoil might affect follow-up shots but will not increase the shooter’s fatigue from shooting.

Strengths and Weaknesses of 300 Blackout vs 5.56

Many people think that 300 Blackout was meant to replace 5.56 entirely. This is not the case. Statistically, 300 Blackout outperforms 5.56 in terms of energy and its use in suppressed and shorter barreled weapons.

This is because 300 Blackout was optimized for use in a compact, suppressed weapon. It shouldn’t be surprising that it outperforms 5.56 in these areas. 

Barriers and dense materials are also more easily defeated by 300 Blackout than 5.56 due to the bullet weights used. This is good for defeating cover and hunting medium-sized game but is not always the solution we’re looking for.

While 5.56 is milder in shorter barrels than 300 Blackout, it does have good ballistic performance out of normal carbine and rifle-length barrels. For example, the M193 5.56 round from our example has a velocity of 3,260 fps with 1,294 ft-lbs of energy when paired with a 20-inch barrel. Even 16-inch barrels will cause similar performance.

Due to current legal restrictions, rifles that would get the most out of 300 Blackout (short barreled and suppressed) are more expensive for the average individual or have to be some form of AR-pistol. This means a rifle with a 16-inch barrel in 5.56 is more accessible for the average individual.  

300 Blackout vs 5.56 Cost and Availability

Ammunition availability is a major factor when selecting a firearm. In terms of 5.56 vs 300 Blackout, 300 Blackout is roughly twice the price of 5.56 on average.

While it has become more available over the years since its release, 300 Blackout is less likely to be available when compared to normal 5.56 offerings. But 300 Blackout can be reloaded onto 5.56 cases if you have the tools available.

5.56 vs 300 Blackout: Which is Better for Home Defense?

While the 300 Blackout has better penetration, energy, and performance at close ranges, that better penetration can cause problems for home defense.

The likelihood of a stray round going through an interior wall and the risk of over-penetration is increased when using 300 Blackout.

5.56 is better for home defense since it is designed to fragment to a degree on impact, lessening overpenetration concerns.

300 Blackout vs 556: Which is Better for Hunting?

For small game and varmints, 5.56 is suitable, especially for coyotes. However, once you start hunting medium game legal restrictions and ballistic concerns point to 300 Blackout as the solution.

In many locations, 5.56 is too small to legally hunt with. Additionally, some animals, like boar, require better penetration ability in order to achieve an ethical kill. The 300 Blackout round with its better energy retention and penetrative abilities makes it extremely useful as a hunting round.

When You Should Use Either 

Which round you should use comes down to the parameters of your task. In those situations where longer shots or home defense are concerned 5.56 is the better option, especially combined with modern projectiles.

In situations where things like boar hunting or similar activities are your primary concern, it is better to use 300 Blackout. This is because of the better ballistic performance and the ability to use shorter suppressed rifles.

Either way, each round has its own role to fulfill and every factor should be taken into consideration to determine which one is right for the situation.

Interested in purchasing some 5.56 or 300 Blackout rounds? We sell both!

Click here to see our 5.56 ammo.

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