Things To Know About Subsonic Ammo

Subsonic 300BLK ammo featuring Norma brass and Hornady projectiles.

As I alluded to last week, the ammo situation out there is pretty sparse, and unprecedented. People are grabbing up whatever they can find, regardless of whether it’s truly appropriate or not. Desperation will make people run full-metal jacket rounds in a defensive role, or they’ll pick up some oddball load and cross their fingers. There’s nothing wrong with new concepts in ammo, of course, but buyer should beware. In your travels, you may run across loads in various calibers marked as “subsonic”. You may ask - “What is subsonic ammo and is it appropriate for my use case?”

There’s no clear answer, but knowing what subsonic ammo (in various calibers) can and cannot do is a good place to start…

What Is Subsonic Ammunition?

Simply put, anything “subsonic” is something that travels below the speed of sound. Subsonic ammunition, by definition, is any cartridge that propels its bullet at a speed that is below the sound barrier. At sea level and a pressure of 1 atmosphere (14.6 psi), the sound barrier is at 761.2 MPH, which is 1116.4 feet per second. For reasons I have yet to discover, ammo makers love to rate their creations in feet per second. I’m guessing since compared to the world as a whole, ammunition really doesn’t go that far, so it’s more scientifically convenient to rate it in FPS - at least here in the US.

So, if your ammunition doesn’t exceed 1116.4 FPS in velocity at sea level, it is a subsonic round. Other than speed, the defining characteristic of a subsonic round is that it will not create a sonic boom along it’s flight path. Much like a high-performance jet aircraft, a bullet going faster than the speed of sound will create a sonic boom.

WMD Guns AR-15

What’s The Big Deal About Subsonic Ammo These Days?

Just by default, subsonic ammunition isn’t anything new. In the days of old, the trend was towards heavy projectiles, such as one of my favorites (of course), the .45 ACP. You can only cram so much powder safely into the cartridge, and the bullet itself had to be of a certain weight to be effective, so big and “slow” was the norm. Now grant it, there are supersonic .45 ACP loads, but those are rare. As time went on of course, the trend was towards small and fast projectiles, such as 9x19mm Luger (and NATO) for handguns, and 5.56mm for rifles. Zipping along at supersonic speeds, the small and lighter loads rely on speed and projectile shape to accomplish their goal.

So why this sudden interest in slowing things down? Simple - suppressors.

If You Run A Suppressor, You Want Subsonic Ammo

As we’ve gone over prior, legally acquiring or manufacturing a suppressor for your own use in our nation is a cumbersome task at best. Despite this, suppressors have been selling at a brisk pace, and moves to deregulate these useful items still continue on.

With a suppressor, you can generally run any ammo you wish out of the host weapon. Subsonic or supersonic, it doesn’t matter - the suppressor will still reduce the volume and report of the shot. What a suppressor cannot do however, is eliminate the sonic crack/boom of a supersonic projectile. This phenomenon occurs outside of the suppressor itself (downrange) and of course the can cannot mitigate it.

With this in mind, the suppressor enthusiasts of the world seek out subsonic ammunition for their firearms. With no sonic boom/crack to worry about, the only noise one will hear is the “clatter” of the gun’s action, the reduced report of the gunshot out of the muzzle end of the suppressor, and the impact of the bullet downrange. Not truly silent, of course, but subsonic ammunition delivers the ideal “quiet” experience for shooters.

Subsonic Ammo Is Ideal For Hunting And Defense

For hunters and sportsman, this is a marked advantage of course - suppressed subsonic shots fired are less likely to startle the game. Also, certain can/ammo combinations are “hearing safe” and one can stalk their prey and keep their hearing about them. Along the same lines, competitive shooters don’t have to deal with the lingering effects of hearing loss.

And yes, in a defensive situation, a suppressed firearm loaded up with subsonic ammo is a true godsend, especially if the emergent situation is indoors. No boom, no crack to be amplified by the enclosed space. You can defend yourself, and keep your hearing (and wits!) about you.

Subsonic Ammo Has It’s Drawbacks

Of course, subsonic ammo isn’t a magical cure-all for suppressor users. From the get-go, you should verify that your selected load will work efficiently in your gun/suppressor setup.

Subsonic Ammo Is Harder To Stabilize In A Gun Barrel

The biggest thing to check is if the projectile will stabilize properly in your firearm. Subsonic loads tend to use heavier projectiles than standard, and your firearm barrel may not have a fast enough twist rate (length per twist of rifling - for example a 1:7 barrel rotates a bullet once every seven inches) to achieve proper stability. In pistols this usually isn’t an issue, but in rifles, it’s critical. Even more so with a suppressor. A wobbling and tumbling bullet can cause a baffle strike or worse in a suppressor. Basically what that means is the bullet leaves the barrel all wobbly-like and starts to tumble end-over-end. Inside a suppressor, this is a disaster as the projectile will mangle the suppressor baffles and could even puncture the suppressor tube. While most suppressor companies will “fix stupid, once” and gladly place new baffles in your suppressor, a tube breach is much more serious. In the US, the suppressor tube is usually the serialized part, and if it cannot be repaired, it must be replaced, even if the baffles are intact. And since it’s serialized a new tube constitutes a new item - thus you have to do the NFA dance all over again. No fun.

Subsonic Ammo May Not Cycle Your Gun Properly

If you are using a single-shot or bolt-action firearm, of course this doesn’t apply since you are cycling the action, and not relying on the blowback to do so. Often, with cartridges not meant to be subsonic, such as 5.56mm, this is a given. There’s just not that much gas coming back, so you’ll have to manually cycle your firearm after each shot. It’s why 5.56mm subsonic is typically marked as “non-cycling” so if you are using it in a standard AR, you know what to expect.

Of course, with cartridges that are naturally subsonic such as .45 ACP, or specifically designed for subsonic use, i.e. 300 BLK, this isn’t an issue. Your firearm will cycle successfully, assuming everything else is in order of course.

For practical use, you should seek out cartridges that are known to be subsonic or designed to be as such to begin with. 300 BLK is an amazing load in this regard.

Subsonic Ammo Is Short Range

While not a drawback per se, one shouldn’t expect to be dinging steel at 2000 yards with a subsonic load of any caliber. The energy simply isn’t there. After about 500 yards, subsonic 300 BLK loses energy considerably. Again, this may not be a drawback depending on your level of skill and situation. A veteran hunter can quietly close in to within 100 yards of his or her quarry and make short work with a suppressed rifle loaded up with the appropriate subsonic ammo. In a common defensive situation, the encounter is often at 10 yards or less, well within the effective range of common purpose-made subsonic loads.

Subsonic Ammunition Is Expensive

OK, these days all ammunition is expensive. But subsonic ammo has always tended to cost more, simply due to it’s limited production runs and specific projectile designs. For example, in the video below from a few years back, I chose to do a full-auto mag dump of 220 grain subsonic Hornady A-MAX ammunition. 30 rounds downrange in less than ten seconds. Fun, sure, but that was basically over $50 thrown into a dirt wall. The things I do for this blog, I tell ya…



If You Suppress, Go Subsonic

Much like any purpose-built ammo outside of plinking and training loads, it’s always good to have a cache of subsonic ammunition lying around for defensive and hunting use. Despite the cost and minor drawbacks, it’s definitely worth it if you have a suppressor.

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