.300 AAC Blackout is hands-down, one of the coolest alternative AR-15 cartridges on the market today. This wicked cartridge is more than capable of dropping whitetails at 100 yards and ringing steel targets farther than that. And when you use subsonic ammo, the loudest sound you’ll hear is the clapping of the bolt.
If you’re looking for an awesome new cartridge for your AR-15, this one should probably be near the top of your list, especially if you’re running an SBR. (SBR stands for “short barrel rifle” in case you were wondering).
Let’s take a closer look at the .300 AAC Blackout to see if it’s right for you.
What is .300 BLK?
.300 AAC Blackout (also known as .300 BLK or 7.62x35) is a cartridge originally developed for U.S. military special operations. Wanting something with better performance than 5.56 NATO, top military officials sought a .30-caliber round capable of ballistic performance similar to the Russian 7.62x39mm (think Soviet SKS and AK-47). They also wanted their new cartridge to deliver effective subsonic, suppressed performance. As if that wasn’t a tall enough order, it also had to be compatible with existing M4 magazines without sacrificing ammo capacity.
All that may only seem possible in the realm of fairy tales. However, along came exotic ammo maker, Advanced Armament Corps (That’s where the AAC comes from), stepping up to the plate with their fairytale cartridge, the .300 AAC Blackout.
Built off the company’s existing .300 Whisper cartridge, the new .300 BLK met every single requirement.
How it Performs
When you first look at the .300 BLK, it seems like a stubby little cartridge, especially when compared to other .30 caliber rounds. It definitely doesn’t look like a long-range performer.
You certainly aren’t going to perform any extreme distance shots with sniper-like accuracy with this one. But that’s not what .300 BLK was designed to do.
When we look at exterior ballistics (how the bullet flies through the air), 5.56 is actually a much better performer than .300 BLK. 5.56 NATO has a much flatter trajectory than .300 BLK, even though .300 BLK has a sleeker, more aerodynamic projectile design.
That’s because .300 BLK travels slower than 5.56. That slower velocity doesn’t allow you to get the full advantage of that beautifully tapered profile. As a result, .300 BLK drops drastically and sputters out after about 250 yards. However, it offers repeatable accuracy on targets out to at least 200 yards.
Where .300 BLK outshines 5.56 NATO is in terminal ballistics (what happens when the bullet hits the target). The .30 caliber bullets in .300 BLK are shorter, fatter, and heavier than those in 5.56 rounds. Without getting into all the physics and math involved in terminal ballistics, the wound created by a .300 BLK round will generally be wider and deeper than one created by 5.56 NATO.
Both cartridges are perfectly capable of creating lethal wounds, especially with modern bullet designs narrowing the advantages of larger caliber projectiles. However, .300 BLK gets a slight inherent edge over 5.56 when it comes to terminal ballistics.
Subsonic Vs Supersonic
The vast majority of ammo you find on the shelves of your local sporting goods store is supersonic. This means the projectiles travel faster than the speed of sound (about 1,125 feet per second at sea level). Anything that travels faster than the speed of sound creates a sonic boom. When you add that sonic boom to the sound of exploding gunpowder, a single gunshot can create some serious noise.
On the other hand, subsonic ammunition propels projectiles slower than 1,125 feet per second, so there is no sonic boom. Add a suppressor to control the gunpowder explosion, and your rifle just became one of the quietest weapons on the face of the planet.
Barrel and Twist Rate
Everything you need to build a .300 BLK AR-style rifle is readily available. You can even convert your existing AR-15 (in 5.56) to .300 BLK without much effort. All you need is a barrel change. You can keep your magazines, bolt, and the lower receiver.
Before you swap out that barrel, it is important to note that .300 BLK burn all their powder quickly, so their projectiles achieve optimal velocity when fired from a short barrel.
A 9-inch barrel is usually considered the optimal barrel length for .300 BLK. This makes .300 BLK perfect for home defense where you may need to maneuver within tight interior spaces.
That short barrel length also comes in handy when you add the extra length of a suppressor onto your rifle.
You also need to consider the twist rate of the barrel on your.300 BLK AR-15. Twist rate is the rate of spin of the barrel rifling. Twist rate is represented by a ratio of inches per turn. For example, many AR-15s feature a 1:7 twist rate. This means the rifling makes one complete rotation over seven inches of barrel length.
A 1:7 or 1:8 twist rate works best with .300 BLK. If you’ll be shooting mostly supersonic loads with lighter projectiles (80 to 125 grains), opt for a barrel with a 1:7 twist rate. Because subsonic loads are made with heavier projectiles (usually 225 grains or more), you may be better served by a 1:8 twist rate.
Summing It Up
While .300 BLK probably won’t be completely replacing .223/5.56 any time soon, it’s hard to beat this newcomer’s versatility. Its performance and quiet shooting make this cartridge particularly well-suited for hunting, home defense, and close quarters combat. If you want to use a suppressor and subsonic ammo to fire lethal rounds through a short-barreled AR-15, you should consider giving .300 BLK a try.