Given the level of interest in the 300 AAC Blackout (commonly referred to as 300 BLK) caliber, and my obsession with unusual chamberings, I thought it would be interesting to take a closer look at exactly what the cartridge does. As one of the intents behind the development of this cartridge was to provide better terminal effectiveness when fired from short-barreled rifles, I decided to do some basic tests along those lines.
Use of a short-barrel configuration instead of a full 16-inch rifle barrel will cause a drop in muzzle velocity up to several hundred feet per second. It’s exactly this velocity drop that caused folks to start looking at alternatives to the 5.56mm NATO projectiles. Much of the effectiveness of that round relies upon its 3,000 feet per second velocity, so when that drops by 500 feet per second or so, it’s not as effective.
For testing, I used a CMMG Mk4 pistol. This particular model features an eight-inch barrel, which keeps it compact and handy even with a suppressor attached. Speaking of silencers, I fired all of these tests with a SilencerCo Specwar 762 attached. That model handles both supersonic and subsonic 300 BLK loads with no problem. I also added a Sig SB-15 Forearm Brace and an Aimpoint Micro T-2 optic for effective close-range sighting. All in that, this is a nice little package.
I also used a 16-inch-barreled Daniel Defense 300 BLK rifle for velocity comparison in some cases.
I chose a variety of loads for this little experiment with performance ranging from light bullet, supersonic velocity to slow and heavy subsonic rounds. Some are off-the-shelf factory loads while others are handloads using common .300 Blackout ballistics. I shot them to measure velocity and through Clear Ballistics gelatin blocks to see what we might expect from different combinations fired from the CMMG pistol.
1. Hornady 110-grain V-Max
Rated at 2,350 feet per second when fired from a rifle, I expected this one to lose about 200 feet per second with the CMMGs shorter pistol barrel. It did, and I measured average velocity from a string of shots at 2,169 feet per second.
V-Max bullets are ideal for varmint hunting as they are supposed to “blow up” in organic targets. This one certainly did, even at the lower velocity generated by the CMMG AR pistol. The V-Max started to blow up about four inches into the gelatin. It left a trail of debris, finally terminating with a good chunk of the base about 17 inches into bare gelatin. The recovered weight of all pieces along the trail came in at 87.8 grains. This last hurrah chunk-let weighed 65.5 grains. As for the rest of the weight? Got me. Perhaps it now resides in Las Vegas with Elvis.
2. Nosler Ballistic Tip 125-grain
I loaded these projectiles with IMR 4227 powder to the higher end of the published range. From the Daniel Defense rifle with a 16-inch barrel, they clocked in at 1,971 feet per second. From the eight-inch CMMG pistol, they reached 1,771 feet per second. This bullet also started to blow up about five inches into the gel block, but a much larger piece traveled about 20 inches deep. The base stayed intact with only the tip of the bullet fragmenting along the way. The recovered base weighed 112.1 grains. Adding the assorted debris brought the total recovered to 114 grains.
3. Hornady SST 125-grain
The SST bullet is not supposed to expand at lower velocities. It’s designed to go deep, with controlled expansion coming from higher velocities. I figured it wouldn’t expand much, if at all, and it didn’t. Using one of my handload recipes, the pistol pushed out the projectile at about 1,737 feet per second. As a reference, fired from the 16-inch barrel rifle, it developed a velocity of 1,915 feet per second. It penetrated to just about 22 inches and retained everything except the ballistic tip.
4. Barnes TAC-TX 110-grain
The Barnes TAC bullets are solid copper designs that are intended to penetrate and expand. I loaded some of the TAC-TX projectiles using H110 powder to a velocity of 2,377 feet per second when fired from the Daniel Defense rifle with its 16-inch barrel. From the CMMG pistol, I measured the velocity at 2,106 fps.
The solid copper projectile started to expand immediately and traveled 20 inches into the gelatin blocks before stopping. The expansion was picture-perfect, and the solid bullet retained all of its weight except the polymer tip. I recovered the tip about two inches into the gel. When I added both tip and recovered projectile to the scale, the displayed weight was back to the original 110 grains.
5. Hornady A-Max 208-grain and Sierra MatchKing 220-grain
I’m grouping these together as performance was similar—by design. The big, heavy bullets, when loaded to subsonic velocities in 300 BLK rounds, are not supposed to expand. In fact, the Sierra MatchKing and Hornady A-Max bullets are not supposed to expand under any normal circumstances. That’s simply not their purpose. The MatchKings have a small hollow hole in the tip, but that’s just a side result of the manufacturing method. The A-Max has a polymer ballistic tip, but again, that’s there to improve flight characteristics, not to aid expansion.
When I shot these into gelatin, the bullets started to tumble almost immediately. Within a few inches, the projectiles oriented base-first and continued along curving tracks through the gel. The whole idea of these is effectiveness through instability, and that’s exactly what I observed.
The bottom line of all this is that it’s important to match your expectations with your equipment. Why are you using a firearm chambered in 300 BLK? Home defense? Hunting? Plinking? Give some thought to what you want to happen when the projectile hits something and choose your ammunition accordingly. Just as important, consider the gun you are using. If you’re using a short-barreled configuration like the CMMG Mk4, be sure to factor in the velocity difference to make sure your ammo will perform as desired.
As the folks at Barnes say, “The bullet is what delivers your intentions to the target.”
Tom McHale is the author of the Insanely Practical Guides book series that guides new and experienced shooters alike in a fun, approachable, and practical way. His books are available in print and eBook format on Amazon.
Images by Tom McHale