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.

The test platform: CMMG's Mk4 300 AAC Blackout Pistol
The test platform: CMMG’s Mk4 300 AAC Blackout Pistol.

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.

Hornady's V-Max load did what it was supposed to, and basically blew up.
Hornady’s V-Max load did what it was supposed to, and basically blew up.

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.

The Nosler hunting round left a large base position that penetrated deep.
The Nosler hunting round left a large base position that penetrated deep.

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.

The Hornady SST is designed for controlled expansion and deep penetration, so as expected, it's not the right fit for a short barrel round.
The Hornady SST is designed for controlled expansion and deep penetration, so as expected, it’s not the right fit for a short barrel round.

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.

If I was using a short barreled 300 Blackout for home defense, the Barnes TAC-TX is what I would choose.
If I was using a short barreled 300 Blackout for home defense, the Barnes TAC-TX is what I would choose.

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.

The heavy and slow subsonic bullets like this 220 grain Sierra MatchKing are not supposed to expand, but to tumble, and they do.
The heavy and slow subsonic bullets like this 220 grain Sierra MatchKing are not supposed to expand, but tumble, and they do.

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

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7 thoughts on “Breaking Down 5 Different 300 Blackout Loads’ Terminal Ballistics

  1. What sort of velocity drop did you see with the 208 and 220 grain bullets in the short barrel vs the longer one? How effective would you guess they are against wild game?

    1. While McHale seldom responds to good questions and writes some questionable material, I can tell you the subsonic rounds are not really meant for going after game, unless you to match the challenge of killing with a handgun.
      You will experience around the 500 foot pound range at muzzle and not very much drop off in energy out to around 100-150 range.
      You will have a fair amount of drop and hitting past 150 starts becoming a fair amount of practice skill.
      I am not able to tell you exactly how much velocity loss you can expect to have from a short barrel, but it is not as much as when you have a supersonic round. What I have been lead to believe is only 50-100 feet per second. However, because of the B.C. of the heavy rounds, it is not much of a disadvantage to terminal ballistics.
      Heavy, long, slow moving bullets tend to just keep going slowly and not shed velocity very fast. The to tend to penetrate deeply however, because a long, slow bullet will have a high sectional density and resist slowing down period.
      Hope that helps you out some.

    2. In my experience there is no velocity loss in short barrels with the subsonic ammunition. The powder is consumed within the first 8″ for the subsonic cartridges and after that the pressure and drag seem to balance each other out and keep the velocity steady. I imagine you would see a slow down after 16″ or so as drag overcomes pressure though.

  2. Sounds like you used 4227 with the SST. You’re not going to get as much velocity with 4227. Try some H110/W296 under that 125gr SST. You should be able to get 1900fps from your 8.5″. Then redo the gel test.

  3. The 30 caliber Amaxs expand even more explosively than V-Max. 155s from my garand at 100 come out the back of a gallon jug or water in fragments.

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