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What Is The Difference Between Subsonic And Supersonic Ammunition?

Subsonic ammunition is specifically manufactured, or loaded, to not break the sound barrier. This ammunition's general purpose is to avoid creating a sonic boom, or in ammunition terms, a sonic crack. Subsonic ammunition is designed for the bullet to maintain a speed that does not create that sonic crack. A bullet traveling below the speed of sound simply doesn't make that sound. Any round that propels the bullet at a velocity below the sound barrier is subsonic ammunition. The typical speed of that is around 1100 fps, as always, depending on conditions. Conditions that could affect subsonic ammunition are the same as the conditions that affect other ammunition; elevation, weather, and atmosphere. Conditions are only a possibility and should not dramatically affect the subsonic rounds. 

Subsonic ammunition may sound futuristic, but the truth is that it has been around for many, many years. Shooters have been handloading their own subsonic rounds since before the term subsonic was used to describe these rounds.

So what's with the rise of popularity with subsonic ammunition? The rise in popularity of subsonic rounds is directly related to the rise in popularity of suppressors. An unsuppressed firearm will make a loud noise due to pressurized gas. Using subsonic ammunition in a firearm without a suppressor still makes the loud sound, but without the high-pitched crack of a supersonic round. 

The loud noise that we hear when firing is caused by the pressurized gas exiting the barrel and the immediate change in temperature as the bullet and gases escape. A suppressor addresses the sound and crack of a shot by adding a larger chamber to the firearm. The suppressor or larger chamber added to the end of the barrel gives the escaping gases a longer and larger chamber which allows it to cool before coming into contact with the external elements or atmosphere. Subsonic ammunition in combination with a suppressor makes it ideal for achieving the optimal performance of your suppressed firearm. 

Unintentionally, some calibers are better for suppression than others. For example, the .45ACP is great for suppression because it is already manufactured with a heavy bullet and for slow-moving subsonic speeds. If you are looking for suppression of your 9mm, look for the 147 or 165 grain loads for the best performance. The most popular rifle round for suppressed rifles is the .300 Blackout. Manufacturers of ammunition are catching on too, and you can now find more subsonic ammo for a wider variety of rifles, especially the newer caliber classifications like the .350 Legend. 

Just as sure as there are some calibers that are better for suppression, there are those calibers that are not great for suppression. Keeping in step with larger, slower, heavier, rounds being ideal for subsonic ammo, the opposite will apply in regards to ammunition that is not ideal for subsonic uses. Any cartridge that has high case capacity in comparison to the weight of the bullet creates high velocity. Some of the most popular calibers for suppression are not great for shooting subsonic rounds, like the .223 or 5.56, after all, why would you pay that much for a rifle only to shoot powered down rounds with a smaller projectile?

Brown Bear 7.62x39 196gr FMJ Subsonic Ammunition


Supersonic ammunition is, well, almost everything else. Subsonic ammunition travels slower than the speed of sound and supersonic ammunition means that the projectile is traveling faster than 1100fps and breaks the sound barrier, which in turn creates that common sonic crack that we hear when shooting. Supersonic ammunition not only creates the sonic crack when exiting the barrel, but it also carries sound all along its flight path because it is breaking the speed of sound. 

Supersonic ammunition is not the optimal selection for suppressed firearms, but you will not be disappointed if you choose to use supersonic ammo with a suppressor. In this case, the suppressor will cloak the blast, but you will still hear the sonic crack. While subsonic ammunition will help you achieve optimal performance for your suppressed firearm, that doesn't mean that you always have to use subsonic ammunition, unless, of course, the manufacturer calls for it. There are a few instances that you may want to use supersonic ammunition even with a suppressor. 

Revisiting earlier statements about subsonic ammo and .223 and 5.56 calibers; subsonic ammunition simply does not have enough pressure to make the AR-15 run correctly. Unless they have enough blowback, AR-15s typically don't work like they should. Another reason you may select supersonic over subsonic is range. Most barrels are designed for the standard velocity of their caliber and are optimized by the twist rate to stabilize the bullet for longer ranges. Subsonic ammunition doesn't always have the velocity to travel long ranges because it is traveling far slower. Because of the heavier bullets and slower speed of subsonic ammo, it is often not stabilized enough to make an accurate shot at long distances. 

Sig Sauer .300 Blackout Match Grade 125gr Supersonic Ammunition


While we are looking at two different types of ammunition in this post, we are actually really talking about suppressors. You can use either type of ammunition with suppressors. If suppression is your only goal, the best performing ammunition with your suppressed firearm will be subsonic ammunition. If you are looking for better accuracy at greater distances, you can still use supersonic ammo with a suppressed firearm. Hunters and homeowners often prefer the velocity. While the supersonic ammunition with a suppressed firearm will not quell the sonic crack, it will control the blast from the firearm.

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