November 8th, 2019
5minute read
Think that fancy new suppressor you bought will silence your gun?
Theres more to it than just that.
But lets start at the beginning.
Slapping a suppressor on your pistol or rifle will not make them silent. It takes more than that to stifle the sound of a round being ripped off.
There are two components to gunshot noise: muzzle blast and sonic booms.
The noise we associate with muzzle blast is a result of pressure differential.
A larger volume of high-pressure gas exits the muzzle all at once and escapes into the surrounding low-pressure air.
With the help of subsonic ammunition, like the American Eagle “Suppressor” line of ammo, you can get gunshot sounds down into a more manageable range.
That creates what we perceive as noise.
Thats why airguns, that have no burning or exploding propellants, make noise when you shoot them.
Thats also why so many of them come with moderators (suppressors) pre-installed.
A quality suppressor and the right ammunition can help keep your hearing damage to a minimum.
Pop That Balloon?
But back to the point.
The easiest way to understand muzzle blast noise is to think of a balloon popping.
And don’t forget to get a good quality, suppressor-ready pistol for your project, like this XD-M OSP with a threaded barrel.
Now think about a balloon thats only partially inflated.
When you pop that, it may only annoy the cat because its not nearly as loud.
Thats because the pressure inside is much lower, so the transition to surrounding air is much less intense.
Now lets talk about sonic booms.
You mean like jets and space shuttles?
Exactly, but on a smaller scale.
But the effect is the same.
As the bullet travels, it carries along its own baby sonic boomlet.
And that generates more noise we can hear.
So, when you shoot, both muzzle blast from pressure and supersonic cracks may generate noise.
Whats Speed of Sound?
The speed of sound varies depending mostly on the ambient temperature.
At 70 degrees, the speed of sound is about 1,125 feet per second.
Youll also hear that speed of sound varies with altitude, but thats more a function of temperature change.
Where I shoot, the speed of sound is about 1,133 feet per second.
For example, Ive chronographed a Springfield Armory XD-M with a variety of ammo types.
Almost all 9mm 115- and 124-gr.
ammo is supersonic while the 147-grain loads are subsonic, usually in the 1,030-fps range.
A Range Officer Elite 10mm Ive been testing flings most 180- to 200-gr.
projectiles at speeds just above the sound barrier.
On the other hand, most .45 ACP loads are naturally subsonic.
Subsonic Ammo
Some ammunition, regardless of caliber, is engineered to be subsonic.
While it may be marketed as subsonic you might also see varieties shown as suppressor loads.
For example, I tested the American Eagle 124-gr.
Suppressor load in that same XD-M and recorded average velocities of 1,078.0 feet per second.
Thats surprising, as with standard ammunition, that extra barrel length would have increased velocity substantially.
Often times, especially with .22 LR offerings, subsonic ammo will have heavier-than-normal bullet weights.
That helps ensure a lower working velocity.
For example, the American Eagle .22 LR Subsonic cartridges carry 45-gr.
bullets while most other standard .22s use either 38- or 40-gr.
Fatter is always slower when the charge is the same.
When you combine a heavier bullet load with a lower powder charge, youll actually get two benefits.
First, you eliminate the supersonic crack component of gunshot noise.
That leaves you with muzzle blast.
Adding a suppressor to subsonic ammo gets fun.
A 22 pistol gets into the 115-dB range.
Just a three-dB increase represents a doubling of noise.
That 30-dB reduction is a huge deal.
You may not know it immediately, but that doesnt make it less real.
Most experts also agree that 130 dB is the pain threshold.
Thats not good either.
Conclusion
The bottom line is simple.
Either use proper hearing protection or find alternative ways to protect your ears when shooting.
Suppressors come to mind, but thats not the whole story.
Using subsonic ammunition is a big benefit.
Using subsonic ammunition with a suppressor is even better.
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