The 5.56mm NATO round has been the gold standard AR-15 cartridge for well over 60 years. It has been the ammo issued to our frontline soldiers for over a generation and has seen combat on 5 continents in the hands of the U.S. Military and our NATO allies.

However, some shooters wanted more out of their AR platform, they wanted the ability to shoot a 30-caliber bullet without switching over to the AR-10 and 308 Winchester.

Enter the 300 AAC Blackout, the successful marriage of 7.62x39mm terminal ballistics with the modularity of the AR platform. It is a potent combination that many shooters have declared superior to the 5.56mm NATO round.

But which round is better?

Does the ballistic performance of the 300 BLK warrant widespread adoption of the cartridge by the military, law enforcement, and civilians?

Or does the stalwart performance of the 5.56 continue to dominate with its long-range prowess, muzzle velocity, and stopping power?

In this article, we will compare the new-to-the-scene 300 Blackout to the tried-and-true 5.56mm NATO in this high-velocity AR-15 shootout. Grab those PMAGs and Aimpoints because we are about to blast away at 300 Blackout vs 556!

What is 300 AAC Blackout? The Dark Ops Wishlist Given Form

The development of the 300 AAC Blackout (designated 300 BLK by SAAMI) rifle cartridge began in 2010 when Robert Silvers of the Advanced Armament Corporation (which was later acquired by Remington) was approached by a member of the US Military "dark ops" community.

The unnamed military customer came to him with a problem that Silvers was eager to solve.

With the widespread adoption of the 5.56x45mm NATO cartridge (civilian ammo designation: 223 Remington) for the M4 carbine, US troops were having to use the round for both long-range and close-quarters combat.

Overall, some special forces units were unhappy with the stopping power that the 5.56 NATO and the 9mm (used in several SMGs) offered during close-quarters combat and he wanted something that had more "oomph". Something along the lines of the 7.62x39mm Soviet round fired through the AK-47.

However, there were some other requirements that this customer needed as well:

1. The rounds needed to fit into a standard STANAG AR-pattern magazine and maintain a 30-round ammo capacity
2. The cartridge case head must be the same as 5.56mm NATO so a bolt change was not needed
3. It had to shoot 30 caliber bullets and mimic the ballistic performance of the 7.62x39mm Soviet round
4. The new rifle cartridge needed to be compatible with short-barreled rifles (SBR, barrels under 16") and be completely functional with a suppressor/silencer
5. Both supersonic and subsonic varieties of ammo needed to be functional for long-range shots as well as close-quarters battle, respectively

However, Silvers was not dismayed, and he returned to AAC to begin work on a new cartridge that would meet all these needs. The search for a host cartridge had begun.

Attempts to integrate new calibers into the AR platform were nothing new to the shooting community. The adaptation of the 6.8 Remington Special Purpose Cartridge (SPC) and 6.5 Grendel into the AR platform were mildly successful; however, they fell short of the mark in several key areas.

The 6.8 SPC and the 6.5 Grendel have a larger case head than the 5.56mm NATO cartridge, so a new bolt was required for the host carbine. Secondly, although both cartridges could be loaded into a standard capacity AR-15 magazine, it could not be loaded to 30 rounds because of the increased case size.

Colt Firearms and other manufacturers had been unsuccessful in adapting a 30-caliber cartridge to the M4 carbine. Complicating matters, the M4 cannot be easily modified to shoot 7.62x39mm Soviet either as the severe case angle causes multiple chambering issues using a standard M4 magazine.

Silvers continued his hunt to find a proper host cartridge for his new round by looking at different wildcat cartridges in the shooting community.

The 300 Whisper was probably the best wildcat cartridge that Silvers encountered, and it eventually became the host for the 300 BLK. However, the 300 Whisper could not simply be adapted to be fired from an AR platform because it did not have standardized loadings with SAAMI (Sporting Arms and Ammunition Manufacturers' Institute).

As AAC/Remington was a SAAMI company, it could not load 300 Whisper ammo. Therefore, Silvers took the concepts from the 300 Whisper and modified it to meet their design specifications.

The new round was called the 300 AAC Blackout (300 BLK or 300 Blackout) and was approved by SAAMI on January 17, 2011.

Although many proclaimed that the 300 Blackout round was going to be another one of those "fly-by-night cartridges" it has since become the 2nd most popular chambering for the AR platform. Converting an AR-15 to the 300 BLK round is as simple as changing the barrel, the gas system, bolt, and magazines remain unchanged. Or you could just swap out the upper receiver for ultimate versatility!

300 Blackout Ammo Specs

Since its approval by SAAMI in 2011, the 300 BLK has exceeded expectations in almost every category.

With an overall case length of 35mm, the 300 BLK has a case capacity of approximately 19.2 grains. The reduced case length was required to allow it to fit into a standard M4 carbine magazine while being loaded with a longer 30 caliber bullet.

300 BLK ammo can be broken down into two different bullet weights, 220 grain subsonic and 110 to 125 grain supersonic.

Supersonic ammo, typically firing a 125 grain bullet, will have a muzzle velocity of approximately 2250 fps and have a muzzle energy of around 1404 ft-lbs. Industry standards list the effective range of the supersonic 125 grain bullet loadings to be 500 yards.

In contrast, subsonic ammo will fire a 220 grain bullet and have a muzzle velocity of around 1000 fps and a muzzle energy of 488 ft-lbs with an effective range of 200 yards.

These two popular loadings really illustrate the versatility of 300 BLK ammo. With a simple magazine change, a shooter can switch from supersonic ammunition and long-range engagements to subsonic ammunition for short range combat.

Furthermore, the 300 BLK was designed specifically to experience a full powder burn when being fired in a 9" short barreled rifle (SBR), preferably with a suppressor/silencer.

Continue reading the full guide on 300 Blackout vs 5.56mm NATO here.