Shining New Light On The Blackout

From its beginnings as a tactical cartridge, the 300 Blackout has found solid footing with predator hunters.

Shining New Light On The Blackout

Hornady’s .300 Blackout SUB-X accounted for these bobcats taken only minutes apart after sunset. Despite a broadside shoulder hit from 100 yards, an exit on the spotted cat (R) was limited to several tiny jacket fragments. (Photo: Steve Markwith)

January’s feeble sun had given way to dim moonlight. Inside my drafty blind the propane heater was struggling, and the dead-quiet night had become a tiresome grind – until a coyote materialized in my bino.

Silhouetted against a snowy backdrop, it was trotting toward a bait pile 80 yards from the blind. I killed the hissing heater, quietly opened a window and reached for the suppressed modern sporting rifle.  

Powering up its night scope, I slipped the rifle through the opening and tried to reacquire the coyote. While panning toward the bait, it suddenly appeared in the scope only feet from the coyote buffet. As soon as the illuminated crosshairs found its mark, I squeezed off a quiet shot. The coyote was immediately tumbled by a heavy subsonic bullet as brass whizzed around the blind’s interior. 

I thought I’d caught sight of a second coyote during the transition from bino to the night-scope and, sure enough, I had. A bit more scanning revealed it, seemingly confused by its napping partner. This one was farther at 120 yards, so I held high in its chest. Within moments, Hornady’s new, ultraquiet .300 Blackout Subsonic load had chalked up a double thanks to minimal disturbance of the area.  

Blackout Background

The .300 Blackout is an evolution of the similar .300 Whisper that appeared during the early 1990s. However, some confusion still exists regarding their subtle differences. The aptly named Whisper offered reliable AR function with subsonic loads for maximum suppressor effectiveness.

Formed from relatively short .221 Fireball brass, the stubby .30-caiber cartridge provided enough room in standard M-16 magazines to accommodate ultra-long, heavy bullets of 200 grains or more. Sufficient operating pressures could thus be generated using the small propellant charges needed to keep velocities below the speed of sound. With the nasty supersonic crack eliminated, the result was a very quiet load! And, because the Whisper’s case-head was identical to a 5.56mm/.223 Remington, conversion was as simple as a different barrel. 

Around 2010, based on military interest, Advanced Armament Corporation (AAC) tweaked the Whisper for improved M-4 function. They also submitted it for SAAMI acceptance, resulting in the .300 Blackout. Dimensions vary only slightly, in a manner similar to 5.56/.223, primarily through the BLK’s slightly-lengthened chamber leade. 

Some confusion has since arisen concerning interchangeability of these cartridges, exacerbated by “Whisper” branded firearms and ammunition. Bottom line: Commercial Whisper loads should safely fire in BLK chambers cut to SAAMI drawings, whereas the reverse could cause problems. This situation is now less of an issue since the .300 Blackout has caught on to the point where numerous ammo options exist. In fact, it was also designed to provide reliable AR function with supersonic loads. Through 16-inch barrels, performance is similar to the 7.62x39 Russian without the need for curved AK-type magazines.  

My serious relationship with the .300 BLK dates to early 2014. AR-15 sales had gone soft after the unprecedented 2013 surge. As OIC of a government firearms unit and driven primarily by tactical interest, I mentioned this caliber to some contacts at a major AR manufacturer. Although intrigued, they had no real experience with it – which led to an experiment. A month later, we stood in the back room of their factory while scratching our heads. I’d arrived with a BLK barrel, which we used to create an upper receiver. Trouble was, no headspace gauges were available, nor cartridges of any type, let alone proof loads. 

In the end, I brought it home for R&D. By that point, since ammo was scarce, I’d assembled reloading dies and the extras needed to build cartridges from shortened, necked-up .223 Rem. brass. Plenty of common .308-diameter bullets, powders and primers were already on hand so, once the laborious case-forming process was completed, testing became a breeze. 

The upper dropped right on to an existing AR lower and cycled with standard magazines. Proceeding cautiously, I encountered no significant problems. This process eventually led to a successful product and, as things turned out, the tactically-oriented research also revealed some unique sporting advantages — particularly regarding predators.

Avoiding the Sound Barrier

Even with the best suppressors, a bullet emits a nasty down-range crack when supersonic. The trick is to keep them below the sonic threshold of approximately 1,125 fps (largely dependent on air temperature)– without compromising semiauto function!

Three Blackout loads (L-R): Hornady 190-grain SUB-X, Hornady 110-grain V-MAX, and Barnes 110-grain TAC-TX. The solid-copper Barnes is topped by a long plastic tip designed to approximate 5.56/.223 cartridge length (R). Note their varying magazine-ribs engagements.
Three Blackout loads (L-R): Hornady 190-grain SUB-X, Hornady 110-grain V-MAX, and Barnes 110-grain TAC-TX. The solid-copper Barnes is topped by a long plastic tip designed to approximate 5.56/.223 cartridge length (R). Note their varying magazine-ribs engagements.

The conundrum is most .30-caliber bullets heavy enough to develop requisite pressures are designed for much higher velocities, negatively affecting expansion. Stability and accuracy also can degrade without extremely quick rifling twists; typically, 1:8, or even 1:7. And, of course, trajectory will be more on the order of a brick, especially beyond 100 yards. However, the advantage is a quiet report.

Thanks to a commercial reloading connection, I was able to gain valuable knowledge before tackling subsonic loads. Using Hornady’s 220-grain roundnose bullet recipe, five shots averaged 1.5 MOA despite minor 100-yard key-holing. Similar results were duplicated as other firearms were sourced (all with 16-inch, 1:8-twist barrels). Suppressed function was reliable in ARs with carbine-length gas tubes, and fouling wasn’t excessive. These were non-issues with a pair of simple break-barrels, which proved to be exceptionally quiet.  

Regarding semiauto feeding, standard AR magazines have interior ribs designed to contact 5.56mm cartridge necks. However, the ribs can squeeze some shorter BLK rounds inward from contact with their chubby bullets. Function beyond 12 rounds can be iffy, so I sprung for several 10-round Magpuls along with 5-round limiters. After tweaking the cartridge length, I had a reliable, state-legal hunting AR – except for one major concern: I just didn’t trust expansion. When hunting at night over bait in heavily wooded terrain, loads that anchor coyotes help. Since expanding subsonics were scarce, I lived with the supersonic crack of a suppressed .223 AR – and waited for a better BLK bullet.  

SUB-X to the Rescue

During June of 2018 while attending a Hornady event, the factory reps broke out their new Subsonic 190-grain SUB-X Blackout load. As ballistic testing progressed, I hovered anxiously until scoring on a bare gel-block shot. Bingo! Penetration — nearly 18 inches — and expansion were as advertised, “meeting FBI protocol for terminal performance through Flex Tip technology.” I left with a cherished box for further testing. 

The box shows 200- and 300-yard drops of 33.4 and 104.8 inches based on a 100-yard zero and 1,050 fps muzzle velocity. Hornady claims velocity will exceed 900 fps throughout; their stated minimum for expansion, but, given the steep trajectory, hits on coyote-sized targets seemed dicey during real-world conditions. For me, those include darkness coupled with a night scope and typically skittish quarry. Fortunately, those issues can be mitigated. In our case, when establishing bait sites, given the challenges of shooting during darkness, we prefer to stay inside 120 yards regardless of the caliber. 

Since such close-range BLK data was scarce, two proven ARs were enlisted in 16- and 10 1/2-inch barrel lengths — both capable of near-MOA accuracy with the SUB-X. After verifying their 100-yard zeros (suppressed, off sandbags), the same targets and aiming points were used at 25, 50, 75 and 125 yards. Chronograph data was recorded at 35 degrees F. The flatter-shooting 16-inch AR averaged 1,100 fps, close to supersonic at that temperature. All rounds struck within 3 1/2 inches of the crosshairs out to 125 yards. 

The 10 1/2-inch AR pistol clocked 1,025 fps. Being night-scope equipped, its trajectory phase was fired in low light. Groups remained tight, but the loopier trajectory gave up 25 yards. At 125 yards, drop was 5 1/4 inches. These results differ somewhat from published ballistic tables, hence the value of actual testing. A number of factors including scope height can skew data. One plus: Previous 220-grain yawing related to the short 1:8 barrel disappeared with 190-grain SUB-X. This eliminated concerns over baffle strikes and accuracy improved dramatically. Reliability was excellent using P-Mags. 

Among other expanding subsonics, Lehigh Defense sells a 194-grain load with a solid-copper bullet. Meanwhile, Sig Sauer has announced a 205-grain, copper, stepped-nose version designed to eliminate magazine-rib interference.

Surprisingly, I’ve noted instances where a SUB-X didn’t exit predators. Still, it’s best to expect them from such loads. Also, cold-weather hunters should test them for any supersonic reports. Lastly, without a suppressor (a moot practice), stoppages are likely. Instead, just go with supersonics.


Fast, light bullets also have value. Those of 110 to 120 grains can add another 100 yards, although fast-twist rifling may dash hopes of sub-MOA accuracy. From a 16-inch barrel, most 110s can be safely pushed to roughly 2,350 fps; similar to a .30-30 Win. firing 150-grain bullets. Although the Blackout can fire such weights (with a possible gain in accuracy), velocity, trajectory and expansion may suffer.

Good news, though! The latest solid-copper bullets are longer than equivalent-weight conventional types. Twist-wise, they behave like heavier bullets. They also provide excellent penetration. Having witnessed FBI Protocol testing of Hornady 110 GMX in bare gel blocks, I was impressed by its 18-inch penetration and expansion. 

A similar bullet I have some live-game experience with is the solid-copper Barnes TSX. Normally, I’d be leery of using 110- or 12-grain .30-caliber bullets on deer, but a TSX won’t unravel. Using similar 110- or 120-grain TAC-TXs, the several bucks I’ve taken all resulted in clean kills. These bullets have long polymer tips that increase their overall cartridge length to that of 5.56 rounds. Barnes sells them as component-bullets, or as Vortex brand ammunition. SIG now offers a similar factory load. Although somewhat pricey, solid coppers can greatly enhance the potential of this small cartridge. 

Another useful bullet is the polymer-tipped Hornady 110 V-MAX, which often yields near-MOA accuracy. Our northern whitetails run large so I’d rather stick with a copper type, but the V-MAX will hammer coyotes (expect exits and pelt damage). 

Supposedly, all of the above will work on hogs. Their suppressed reports will generate sonic cracks, somewhat similar to high velocity .22 LR from a rifle.


If 110s are zeroed about 2 inches high at 100 yards, 200-yard impacts will be roughly that amount low. Although some may entertain longer ranges, energy and expansion become worrisome. For humane sporting purposes, consider the Blackout a short- to midrange cartridge.

Using a 16-inch barrel, if zeroed per above with supersonic 110s, subsonic bullets may strike a foot beneath the aiming point at 100 yards! Short-barrel difference can be less; around 7.5 MOA through my 10 1/2-inch AR. The explanation is a narrower velocity spread. Although supersonic speed is compromised, subsonics give up little; one benefit of miniscule and rapidly consumed powder charges (actually, even the supersonics are forgiving, compared to short 5.56 barrels).

Fortunately, today’s optical systems offer practical compensating solutions for the disparate trajectories. Some even have BLK-specific reticles. I prefer to dial zeros, but many generic-type reticles will also suffice.

Closing Tips

The Blackout offers intriguing reloading possibilities, using readily available propellants. The ever-popular handgun powder, H-110, is a good supersonic choice, and AA1680 works for subsonics. The internet has how-to videos for those interested in forming brass from shortened .223/5.56 cases, but the Whisper was developed from .221 Fireball brass for a reason: Case uniformity! Using the former, brass thicknesses can vary enough to lodge some necks in BLK chambers. Experiment and buy a chamber gauge before committing to production. 

Concerning ARs, distinctive magazines can prevent the catastrophic effects of firing BLKs in 5.56 chambers! Switch-top (or multiple) AR owners should install “300 BLK” dustcovers. Regarding reliability, a well-established manufacturer is the safest bet given the nuances of suppressors, gas tubes, buffers, etc. 

Of course, bolt-actions or single-shots are immune from such concerns, and some are fairly affordable. Shop for a threaded muzzle and the suppressor can come later. Meanwhile, being no noisier than most .223s (and with similar felt recoil), the BLK has potential for new and/or recoil-shy shooters. 

Western hunters will probably seek flatter shooting calibers that offer more range. However, in the heavily forested east, or over hog feeders, etc., the Blackout can fill a niche — especially if suppressed.


Comments on this site are submitted by users and are not endorsed by nor do they reflect the views or opinions of COLE Publishing, Inc. Comments are moderated before being posted.