What Is Subsonic Ammunition & How Does It Work?

What Is Subsonic Ammo?
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What Is Subsonic Ammunition & How Does It Work?

Everything You Need to Know about Subsonic Ammo

Subsonic ammunition, despite existing as long as firearms have, is currently experiencing a bit of a renaissance.

Over the past few years, rounds that operate in the subsonic range and even rounds specifically designed for optimal performance in this range have increasingly been available on the market.

But why the sudden resurgence? What is the point of subsonic ammunition, and do you need or want it? While it isn't an overly complicated subject, there is plenty to discuss regarding subsonic ammo.

What Is Subsonic Ammo?

Subsonic ammunition is ammunition specifically manufactured so the round doesn't break the sound barrier. It's designed to travel at speeds below that of sound, hence the name subsonic.

That threshold is somewhere around 1,126 feet per second, so most modern rounds and loads break that barrier by default.

The most common 9mm round, for example, is a 115 grain round that usually clocks in at about 1250 FPS.

Why Would I Want Subsonic Ammo?

The purpose of subsonic ammunition is to avoid the crack from the round breaking the sound barrier.

But why would someone want that? The most obvious answer might seem to be for a quieter shooting experience.

However, with standard shooting, subsonic ammo won't likely make a noticeable difference in the sound you hear.

The biggest reason someone would want subsonic ammo is if they're shooting with a suppressor. When paired with a suppressor, the difference in volume is night and day.

While it isn't in any way as quiet as it's portrayed in movies, it is possible for a suppressed subsonic round to not even sound like a gunshot.

Since the suppressor quiets the explosion and expansion of gasses, without the subsequent crack of the round breaking the sound barrier, the resulting firing can sound like random noise instead of being distinctly heard as a gunshot.

This can come in handy for all kinds of settings, from target shooting to hunting or self-defense — reducing your sound profile from "that was a gunshot" to "what was that?" has its benefits.

And while it's still not advisable to shoot regularly without hearing protection, a quieter shooting experience is definitely beneficial to your long-term hearing preservation.

How Does It Work?

The primary method for making rounds subsonic is to make them heavier.

It’s simple physics: The heavier the object, the more force is required to generate speed, so to make subsonic rounds manufacturers just make them heavier.

What Rounds Are Subsonic?

Some rounds are naturally subsonic. Older rounds that have existed prior to more modern guns, for example, will likely be default subsonic.

The oft-discussed .45 ACP is one such round due to its size. The .45 is big, fat and slow (me too, .45, me too) so it's by default not breaking the sound barrier no matter what type you buy.

Similarly, a .9mm round in 147 grain will typically be subsonic just by nature of the bullet weight.

Essentially, anything that you want to buy for your firearm that is below 1100 FPS will pretty much be subsonic. Elevation and weather conditions can apply, so if you're wanting to be sure, slower is better.

There are also rounds that have been specifically engineered to perform as subsonic.

The .300 Blackout was specifically designed to be fired subsonic using a suppressor while maintaining peak performance.

Of course, no one is suggesting that you need to switch to a .300 Blackout setup as your only subsonic and suppressed firearm; it’s just good to be aware that it was created specifically for that purpose.

What Else Do I Need?

There really isn't much required for shooting subsonic rounds.

As we've discussed, some are that way by default and don't require anything else. There are a couple of considerations to keep in mind regarding subsonic ammunition, though.


Because of the heavier round, you might run into some issues with your firearm failing to properly stabilize the round. In most cases, this will be due to a longer twist rate.

The twist rate for a gun is the amount of distance the round must travel before making a complete rotation.

For Modern AR-style rifles, you'll often see anything from a 1:7 to a 1:9, which means one rotation per 7 or 9 inches respectively. If the twist rate of your gun is on the upper end of the spectrum, it could have trouble stabilizing the round.

The easiest way to ensure your gun is properly stabilizing rounds is to fire a few without a suppressor on to paper to see how they're grouping.

If they're grouping the way your standard rounds do, you should be good to go. If not, you may run into issues if you try to shoot suppressed.

If the round isn't being properly stabilized by the barrel, when you attempt to attach a suppressor, things can go wrong.

If the round isn't coming out stabilized, it could impact the baffles in your suppressor, causing damage to your suppressor — or worse, damage to you. But again, if your barrel twist isn't too slow, it will stabilize and this won't be an issue. Always test beforehand to be sure.


Another problem that could potentially arise when shooting subsonic ammunition is a failure to properly cycle.

Since the round is heavier, it's moving slower, and that means there's less energy coming out of the barrel. If there's less energy going forward, there's less energy going backwards as well.

Because of this, it's possible that you may run into issues with your firearm cycling properly.

Depending on the type of gun, the ammo you're using and even the fitment of the suppressor, you could see a failure anywhere along the cycling of the gun — failure to fully recoil, a failure to eject, a failure to feed or a failure to go back into battery — any of these could happen.

The better the ammo and suppressor fitment, the less likely these become, especially with a fast-enough barrel twist. But it's still something to be aware of.

For rifles, this isn't necessarily much of an issue. If you do encounter this, you've essentially made your semiautomatic rifle into a bolt action.

While not optimal, it isn't the end of the world, depending on how you're shooting. For handguns, though, this can be considerably less fun and can lead to a more fatiguing shooting experience, both mentally and physically.

Again, with proper ammunition and a gun by a reputable manufacturer made to modern standards, this really shouldn't be a problem in most cases.


At this point, it kind of goes without saying that to really get the full impact of subsonic rounds, you should probably be using them in conjunction with a suppressor.

Suppressors are currently legal for private ownership in 42 out of 50 states in the U.S. Only California, Delaware, District of Columbia, Hawaii, Illinois, Massachusetts, New York, New Jersey and Rhode Island do not allow suppressors for individuals, so if you're outside these states, you're good to go.

Not all states that allow suppressors allow them for hunting, though, so check your local laws prior to using one.

Obtaining a suppressor is pretty straightforward, but there are additional forms and an additional tax you have to pay.

That shouldn't come as a shock to anyone, though. From the moment you make your first firearm purchase, you begin see just how much Uncle Sam has thrown himself into the process.

Also, in typical government fashion, it's a slow process. Once you make the purchase and the forms are submitted, it can take weeks to months before you get word that your purchase has been approved.

To some, that's enough of a turn off to prevent them making the purchase, which is understandable. However, you would be hard-pressed to find anyone that didn't grin ear-to-ear shooting subsonic rounds suppressed the first time.

Other Considerations

Finding rounds that are subsonic can be fairly easy as they are made by most manufacturers, especially given the recent resurgence in their use.

Some calibers are naturally a better fit for use with suppressors, so be sure to keep that in mind.

Additionally, with the option to hand-load ammunition being easily accessible and affordable, always remember that you can load your own subsonic ammunition.

Whether you choose to explore the world of subsonic ammunition or not, it's still a good idea to have a basic understanding of what subsonic ammunition entails.

The more knowledge you have as a shooter, the better a shooter you become. As they say: Knowledge is power, even if it's a bit underpowered, as is the case with subsonic ammunition.

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C. Earls
Thank you AD. Informative and succinct.
Robert Morris
Am in learning process love this information