Review: .300 AAC "Blackout"

This topic is one that has come up a number of times with friends and family, particularly when discussing the AR-15 platform.  The .300 AAC Blackout cartridge (known simply as ".300BLK" on the forums) is a relatively new arrival, and has steadily been gaining a following in the enthusiast world.

First off, I'll share the basics of the cartridge.  This is essentially a trimmed-down .223/5.56 case, necked down to accept a .30 caliber projectile.  The overall length of the cartridge is only slightly shorter (.4mm shorter, to be precise) than that of a 5.56 round, although the projectile is significantly larger.  The beauty of this design is it's simplicity; a .300BLK rifle requires only a barrel replacement, every other component is identical to those in the more common 5.56mm and .223 caliber iterations of the AR15.

I would like to point out a problem I see with this, and let this serve as a warning.  A .300BLK round is shorter in overall length, and can possibly chamber fully in a 5.56mm/.223 caliber rifle.  This means that it's possible to mistakenly put a .300BLK round into a magazine with .223 ammo, chamber the round, and fire the weapon, which would likely result in significant damage to the weapon, and possible injury to the shooter.  This is why, when I go to the range, I make sure the ammunition for the .300BLK is kept separately from any other caliber, and I pay close attention when loading magazines.  I am not speaking from experience here, I haven't blown up my rifle by mistakenly loading the wrong cartridge, but this is an issue I have heard about happening at least once before.

Now that that's out of the way, let's talk a little bit about the ballistic properties of the round.  This cartridge is available in a number of different bullet weights, most common being 115gr. and 125gr.  A standard 5.56 NATO cartridge has a bullet weight of only 62gr.  Since the Blackout was designed as a .30 caliber solution for the AR15/M16/M4 platform, the ballistics are most frequently compared to those of the original AR15 caliber, the 5.56mm NATO.

For comparison's sake, let's briefly review the ballistic properties of a common AR15 variant:

Caliber: 5.56mm NATO (62gr. FMJ-BT)
Barrel Length: 16 Inches
Effective Range: 500 m (Point Target)
Bullet Velocity: 2,927 ft/sec.
Energy: 1,303 lb/ft.

And the same rifle, chambered in .300 AAC Blackout:

Caliber: .300BLK (125gr. UMC)
Barrel Length: 16 Inches
Effective Range: 460 m (Point Target)
Bullet Velocity: 2,215 ft/sec.
Energy: 1,360 lb/ft.

As you can see, the velocity is lower, as expected, for the .300BLK.  Energy is higher, but in terms of bullet drift and drop, the Blackout experiences both at a shorter distance than that of the 5.56.  The 5.56, being a much smaller/lighter projectile, doesn't carry as much energy moving past it's effective range, however.  The .300BLK above carries the same amount of energy at 700 m, that the 5.56 cartridge does at 500 m.  The projectile size and energy increase of the .300BLK also allow for greater penetration of "hard targets" than the 5.56.

Another benefit of the .300BLK is that the original project goals specified that it be suitable for use in a short-barreled carbine outfitted with a Suppressor.  A 220gr. subsonic .300BLK is a fantastic round for suppressor use, especially when coupled with a short barrel.  With a quality suppressor mounted to a 9" Barrel, you can expect a reduction to approximately 130-135 dB, which is below the 140 dB "Safe Threshold" for unprotected hearing.  Supersonic loads, however, are significantly louder, even when using a suppressor, and may result in hearing loss if proper hearing protection is not used.


I will elaborate more on this cartridge, including photographs, within the next several days.  I have only one AR15 in my collection now, which is chambered in .300 BLK.  I made the switch just over a year ago, and I haven't looked back.

Stay tuned for more updates!