By Will Dabbs, MD
If it’s possible for a firearm cartridge to be transformational, then the .300 AAC Blackout is the most transformational round in recent memory. AAC is shorthand for Advanced Armament Corporation, the company responsible for this novel design. The .300 AAC is also known as the .300 Blackout, or BLK. The .300 Blackout is arguably the most versatile rifle cartridge ever devised. Still, many shooters want to know how fairs the .300 Blackout vs. 5.56.
Distilled to its essence, the .300 Blackout is a 5.56mm cartridge case shortened and adapted to accept a .30-caliber bullet. By utilizing bullets of various weights, the .300 BLK can offer either subsonic or supersonic performance out of the same host rifle. This makes the round appropriate for a wide variety of applications.
The 5.56×45 is also offered in numerous bullet types and weights. It is great for use in hunting a variety of game, as well as self-defense. However, most companies only offer it in supersonic speeds. Sure, the 5.56mm can be suppressed but not as well as the .300 BLK.
Bringing About the .300 Blackout
The .300 BLK began as a request from a U.S. special operations unit. These Tier 1 shooters wanted a round they could use in a standard M4 rifle without having to exchange bolts or sacrifice magazine capacity. In 2010, Robert Silvers at AAC produced the 7.62x35mm/.300 BLK using the .221 Fireball as a foundation. Eventually, the round trickled down to American civilian shooters.
Stuffing .30-caliber power into a standard AR had been tried before. Adapting the M4 to fire the M43 Combloc 7.62x39mm round isn’t terribly difficult. However, those big tapered cases demand a weird, sharply curved magazine that really doesn’t fit well into a standard M4 lower receiver. They can also foment undue bolt wear.
Other rounds, such as 6.8 SPC and 6.5 Grendel, worked OK, but they were fat and precluded full capacity magazines. The .300 BLK addresses all of those issues. All that is required to convert most any standard 5.56mm AR-pattern to fire .300 BLK is a new barrel. The converted rifle uses the same magazine and bolt carrier group. SAAMI (Sporting Arms and Ammunition Manufacturers’ Institute) approved the new cartridge in January of 2011.
Stoner to .300 Blackout
Six Degrees of Kevin Bacon purportedly connects every major figure in the history of film to the actor Kevin Bacon. Similarly, a shocking amount of modern American riflery owes its origins to Eugene Stoner. In addition to being the chief engineer behind the ubiquitous AR-15, Stoner also developed the radical round it fired. Stoner, in consultation with Frank Snow of Sierra Bullets, originally designed the .222 Remington. The .222 begat the .223, which eventually begat the 5.56x45mm. This zippy little .22-caliber round has served the U.S. military since the early 1960s.
Alongside a few others at the tiny little ArmaLite Company, Stoner contrived the AR-10 that became the AR-15 that became the M16. Several design evolutions later, that M16 morphed into today’s M4 carbine. Tens of millions of semi-auto variants equip American shooters today. The AR-15 rifle is the most popular long gun in the country.
Nowadays, Stoner’s basic chassis has been adapted into a handgun, a precision sniper tool, a submachine gun and a sporting rifle. The addition of the .300 BLK has breathed fresh life into all of that. By adding a decent sound suppressor and tweaking the load, a .300 BLK AR-15 becomes much more than anything Stoner and company might ever have envisioned.
Specifics of .300 Blackout vs. 5.56
Relatively lightweight 125-grain .300 BLK bullets out of a standard 16-inch barrel will cruise at around 2,200 feet per second. Heavier 220-grain projectiles clock about half that. Both loads are comparably reliable. There are lots of other options, but these are the main ones. Thread a decent sound suppressor on the snout and get ready to have your world rocked.
The speed of sound in dry air is 1,125 feet per second. A bullet traveling faster than that number invariably creates a loud sonic crack irrespective of a sound suppressor. This noise is created by the bullet in flight, not the rifle from which it was fired.
By contrast, bullets traveling slower than that threshold number do not produce a sonic crack. The fast bullets carry enough downrange horsepower to reliably drop a whitetail. The slower sort are not quite movie quiet, but they’re close. By swapping out ammunition in a .300 BLK AR rifle, you can use the same gun to project either power or stealth. A 125-grain bullet fired from a 16-inch barrel purportedly carries the same energy at 700 meters as a GI-standard M855 5.56mm round does at 500.
Rifle & Ammo Availability
Lots of folks make .300 BLK ammo. High-end bullets have all the bells and whistles. An economy of scale makes imported steel-cased versions cheap enough for recreational range practice. Any reputable .30-caliber sound suppressor will easily manage the pressures of the .300 BLK. Many 9mm cans are rated for .300 BLK as well.
If you already have a standard 5.56mm AR-15, all that is required to convert it to fire .300 BLK is a new barrel. Complete uppers are plug-and-play and are obviously therefore more convenient. Most AR rifle producers offer factory-built guns in .300 BLK.
The Rattler from SIG SAUER warrants special mention. This piston-driven micro carbine was designed in response to a request from USSOCOM (United States Special Operations Command) for a tiny suppressible personal defense gun. SOCOM first bought the gun in May of 2022. Though spendy, the Rattler represents the current state-of-the-art technology.
Joys of Trigger Time
The Rattler is indeed unnaturally compact. Given its adjustable gas system, it is also utterly reliable with any .300 BLK bullet weight. Swapping between supersonic power and subsonic stealth is really as simple as exchanging magazines.
The Ruger American bolt-action rifle offers all that wonderful .300 BLK versatility in an accurate budget-friendly platform. The muzzle is threaded 5/8×24 for a standard .30-caliber sound suppressor. Recoil is positively recreational. When equipped with a good can, the gun is actually hearing safe when fired outside without muffs or plugs.
As both the 5.56mm and .300 BLK share the same magazines, care must be exercised not to mix up the rounds. The barrels look the same on the outside. Luckily, 5.56mm won’t chamber in a .300 BLK gun due to the shoulder geometry of the case. By contrast, the bolt will not readily close over a .300 BLK round in a 5.56mm barrel due to the larger diameter bullet. However, I have seen the remains of one rifle wherein the shooter forced the bolt home, shoving the bullet back into the case. He subsequently transformed his expensive AR-15 into a bomb. Don’t be that guy.
Both the .300 Blackout and 5.56mm are fun on the range and effective for both hunting and home defense. And they are similar in many ways. Everything you need to break into the exciting world of .300 BLK, from barrels to suppressors to complete rifles and ammo, is just a click away on GunBroker. Investing in a decent sound suppressor and a .300 BLK host will change the way you shoot.
