The .300 Blackout is an effective round that bridges some of the wide gap between a .223 and a .308 as well as allowing an AR15 platform rifle to encroach on the ballistics territory of the venerable AK 47. Plus the 300 BLK has the benefit of easily going subsonic making it about as quiet as possible given the mechanical noise of operating a rifle’s action. Adding to the quiet excitement is that the difference between a traditional AR15 in .223/5.56 and one in 300 BLK is little more than a barrel swap. That’s right, everything else might be interchangeable between the two.
Chicken or Egg?
Wildcat cartridges can successfully address niche ammo needs, but unless the specific cartridge was blessed by Sammy (properly SAAMI or Sporting Arms and Ammunition Manufacturers’ Institute), the cartridge would not get the widespread support needed to be taken seriously by the big gun and ammo manufacturers let alone the general shooting public. AAC, or the Advanced Armament Corporation in collaboration with Remington Defense ironed out the kinks in the wildcat .300 Whisper cartridge getting formal SAAMI joy in 2011 which is why the .300 Blackout still has that new car smell.
The .300 Blackout is a 30 caliber solution that grew from a set of needs not the least of which included the use of existing AR-style magazines while maintaining the same mag capacity, the use of M4-style platform uppers and lowers; being ballistically similar to the AK 47 round of 7.62mm x 39mm, and be a higher-mass barrier-penetrating bullet while maintaining low recoil and high performance through short suppressed barrels. Oh, and best of all, easily running both supersonic and subsonic in the same rifle with absolutely no change in the gun. In fact, it is this latter capability that 300 BLK owners find most attractive. So the .300 Blackout can drop a deer at 200 yards, or lob 30-cal lead downrange with little more noise than a cycling bolt.
AK 47 rifles are near impossible to run subsonic due to the gas system. And they are certainly not able to interchange between supersonic and subsonic on the fly. Major adjustments and tuning would be needed. In the case of the .300 Blackout, it is a cartridge deliberately made to run flawlessly in an AR rifle in both subsonic and supersonic. In fact, the high bullet weight of the subsonic 300 BLK ammo is not just to slow down the bullet (F=MA in Newtonian physics) but also to provide enough of an equal and opposite force to cycle a traditional AR bolt and buffer (Newton’s Third Law of Motion).
While the initial ballistics of a 300 BLK running subsonic are very similar to a .45 ACP, the bullet shape of a .300 Blackout provides a much better trajectory and deeper penetration. A 220 grain 45 caliber slug flying out the pipe of a handgun designed prior to 1911 is much like a forty-five caliber musket ball. On the other hand the .300 Blackout behaves more like a 7.62×39 round causing death hundreds of yards away. A .45 ACP will bounce off cowhide at distance while the 300 BLK should still shatter bone.
300 BLK ammo in the supersonic variety did pass my Walmart test. That means it is sitting on the shelf at the local Walmart right now. However, I was unable to locate any subsonic .300 Blackout ammo at the any nearby Walmarts. Of course subsonic 300 BLK ammo was available at almost every gun store and big box sporting goods store I checked so the stuff is common. And the Walmart gun clerk did say they’ve had 300 BLK subsonic ammo in stock before, but it was elusive as 500 round bricks of .22 long rifle.
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The ammo choices for 300 BLK in supersonic was varied across price and performance. I found plenty of boxes of 20 from $16 all the way up to almost $50. Subsonic rounds hovered around $20-$25 and there was rarely more than one choice at any given store.
Changing a .223 AR 15 into a .300 Blackout can be as simple as swapping barrels. The complete upper, lower, magazines and gas system might work just fine with the 300 BLK. Usually there are a couple other parts that get changed out as well, but truly in a nutshell, it is just a barrel switch. So a best-case conversion to turn your .223 AR into a .300 Blackout is 1) remove your .223 barrel, and 2) install a 300 BLK barrel.
Changing barrels on your standard direct impingement AR is fairly straightforward, but does require some tools. The undeniable tool is a barrel wrench which is usually part of a multi-function armorers tool like the Magpul Armorer’s Wrench. But in order to turn the barrel nut, you must remove the gas tube. And in order to remove the gas tube, you will need to remove the gas tube cross pin using a 5/32nds punch (gently push it out from left to right).
With the gas tube removed, you can unwind the barrel nut freeing the barrel from the upper receiver. You can reuse the gas tube if its in good shape and the right length, and maybe even reuse the gas block as well assuming it works with your barrel and handguard. In my case, I opted for a new low profile gas block because I am going from a Magpul MOE polymer handguard mounted on a 5.56 barrel with an A2 (triangular) front post. The Midwest Industries free-floating handguard I’ll be shrouding the 300 BLK barrel with will need a new gas block. So it was Yankee Hill to the rescue.
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Backing up for a minute, there is an essential tool that makes barrel removal and installation every so much easier and that is an upper receiver vise block. The vise block is a blockish clamp that wraps the upper receiver like a glove allowing the whole unit to be clamped in a vise without concern of damaging or warping your upper receiver. Add a torque wrench to round out your toolset and you’re as good as done.
The .300 Blackout went into military service in July of 2015 when the Netherland’s Dutch Maritime Special Operations Force (NL-MARSOF) ordered 195 carbines chambered in 300 BLK. According to an uncited Wikipedia article on the .300 Blackout, it has an effective supersonic combat range of about 500 yards. Flying subsonic, 200 yards is pushing the limits of effectiveness outside of threats made of paper. Now before anyone goes all sniper on me, most folks, and let’s be honest here, are not able to shoot reliably to 500 yards even under ideal conditions. In fact, 200 yards is a very reasonable and ethical hunting distance. In my particular case, I intend on hunting with this rifle in thick woods where a 50 yard or less shot is common. I grew up hunting in such places with a Winchester Model 94 30-30 which is an excellent “brush gun” as we liked to call them. Iron sights were plenty good at these distances.
I also intend to hunt with a suppressor, or silencer if you want to retain the original name that its inventor Hiram Maxim called them back in 1902; the “Maxim Silencer” to be exact. On a side note, a movie in 1946 was made about Hiram’s life and titled “So Goes My Love.” But reading about the movie, it doesn’t sound like there is any gunplay in it, let alone any silenced fire.
Factory loads of 300 BLK come in several popular bullet weights. In general, those bullets over 200 grains slide down the pipe under the 1100 feet per second speed of sound while anything lighter breaks the sound barrier with a boom. Since most of the powder is burned within the first nine inches of barrel, near total performance can be achieved in very short barrels. To avoid paperwork and a tax stamp and months of delay, I opted for a 16” barrel literally off the shelf at a local gun store.
I already had a SilencerCo Omega suppressor so adding a can to this build was a no-brainer. In fact, that Omega is most of the reason I went down the 300 BLK road in the first place. A suppressed subsonic .300 Blackout literally is only as loud as the bolt cycling and bullet impacting.
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All this is not without a problem. And it’s potentially a big one. A .223 or 5.56 round will cycle into a 300 BLK barrel, and possibly the reverse is true. This means you have to practice proper ammo management. At no time can you risk mixing up or mixing together your mags or your ammo.
There are various solutions and products to keep your ammo act together. The Blackout Band is a silicon bracelet you wrap around your 300 BLK mags. Some folks run different colored mags, while others mark their mags in personal ways. I chose to dedicate Magpul’s sand colored mags to my .300 Blackout with the intent to dye them later to a more fun and useful color. So at the moment, white mags for the Blackout. No exceptions. There is an ever growing number of tales where someone had a loose 300 BLK round that found it’s way into a .223 mag only to blow the gun apart when it was stripped off the top of the mag by the bolt and the trigger was pulled.
And as I noted in my review of the Magpul D-60 drum magazine, not all ammo containers for the .223/5.56 platform are completely interchangeable. In fact, some are downright dangerous. But since .300 Blackout ammo is easily twice to three times the price of .223 rounds at a minimum, getting sloppy with Blackout ammo shouldn’t be a popular problem.
It should go without saying that a 30 caliber subsonic suppressed round with a 200 meter range should have endless uses. Hunting is obvious as is protection. But let’s put a finer point on that protection thing. A bolt cycling is noisy but only within a very limited sound radius. Add snow or thick brush or trees and the noise of a buffer spring boinging and bolt clanking will not travel far. And the thump of bullet impact is evidence that it’s too late to do anything about it. Unfortunately, the 30 caliber bullet leaving the muzzle under the speed of sound drops like a mountain pass after a hundred yards, and like a double-black diamond ski slope at 200 yards. Beyond that it’s ballistics curve would be a boat anchor.
The Downside of Loud
And speaking of sound suppression, if you ever plan on popping off a round indoors, you will want to minimize the bang or risk temporary disorientation and permanent hearing damage. Sorry to be a buzzkill here, but I do have trouble taking seriously anyone who plans on using a short-barreled AR or AR pistol with spiked muzzle brake as a home defense weapon. One boom and it’s all over for most involved. Better get that first shot right because you will be too stunned for a follow up shot. Kind of like flash-banging yourself and loved ones.
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Just as a gas-powered generator makes an unwanted and unavoidable racket, and a campfire makes unwanted smoke and smell, firearms make unwanted noise. So having a silent solution with more umph than a pistol is a good thing. And when things do go noisy, you have a 500 yard solution at your index finger’s fingertip.
Given that the 300 BLK is still young enough to have spots it’s not surprising that reloading your own brand is the go-to option for the more-than-curious. There are limited factory ammo options for subsonic bullet designs often leaving the big game hunter to settle for either throwing projectiles faster than sound or launching barely hollow-pointed varmint rounds downrange to settle the score. But the big news here is that there is actually a selection of subsonic 300 BLK ammo on the shelves of the big boxes. So something’s going in the right direction these days.
Let’s see how this all works out. Stay tuned for Part 2.
All photos by Doc Montana
This article is for informational purposes only, please consult a gunsmith before you make any changes to your rifle.
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