Airgun powerplant noise - which guns are louder and why
by B.B. Pelletier
Happy New Year! I have several questions from last week to answer, so I'll start with this one from dsw, "How does the noise factor play out? I know springers can't be altered for lower sound levels effectively, what about the others?" As I mentioned in my brief answer, I've already touched on airgun sound levels in some other posts, but today I will address the question in whole.
Where does the noise come from?
Two places, and one may be a surprise. First, the compressed air or gas that exits the muzzle causes a blast in the same way gunpowder does - by compressing the ambient air into a blast wave. Firearms differ in the loudness of their reports proportional to their power and the length of their barrel. A short barrel makes more noise than a long barrel, given the same conditions at firing (same cartridge, same loading, etc.). So it is with airguns.
The easiest way to demonstrate this is to shoot an AirForce Talon SS without its muzzle cap. The SS has a 12-inch barrel and makes one heck of a loud pop! Now, replace the barrel with an optional 24-inch barrel and see how much the pop is reduced. That's because the compressed air had more time to expand and use up energy in the longer barrel. That energy was transferred to the pellet in the form of increased velocity. When the air exits the 24-inch barrel, it is at a lower pressure than it was when exiting the 12-inch barrel - hence, the lower noise. The only reason the Talon SS is considered quiet is because that muzzle cap strips away a lot of the turbulent air after the pellet leaves the rifle's true muzzle, which is buried several inches deep in the frame.
If barrel length is the determinant, why aren't all pistols louder than all rifles?
Don't mix apples with oranges. An air pistol will be quieter if it uses LESS AIR for the shot! But, if the same amount of air is used, the shorter barrel will be louder. I experienced this when I was testing the effects of barrel length on velocity with a certain CO2 rifle. Every inch I cut from the barrel made the pellet go slower, but it also made the muzzle report grow louder. I went from 20 inches down to 2 or 3 inches, as memory serves. By the time the barrel was down to a stub, it was REALLY loud.
So what makes the loud noise?
High-pressure gas, such as air or CO2, is what makes the noise. The more there is, the louder the airgun. The powerful Korean hunting rifles such as the Sam Yang Saver Carbine 505 (ESPECIALLY the carbine!) and the AirForce Condor are VERY LOUD! On the other hand, Daisy's 747 Triumph Match single-stroke pneumatic target pistol is very quiet because it uses only one stroke of air and the barrel is very long. See how this shapes up?
Where do spring guns fit in?
As I mentioned last week in the post on Airgun power with light and heavy pellets, spring guns do not produce a large volume of air. This small volume is pretty well used up by the time the pellet exits the muzzle, making spring guns the quietest of all powerplants. Ahhh - but dsw said he knew they couldn't be altered (the sound lowered), when, actually, they can! First, you can add a baffle-type silencer to the barrel and reduce that sound. The TX 200 has this built in at the factory. However, the TX 200 isn't a loud gun to begin with, so the value of this technology is really lost, for as little as it does.
But, your springer will still sound loud to you.
The other noise spring guns make is the sound of the moving parts inside the gun. There's a coiled mainspring releasing and vibrating, a steel piston flying forward and also vibrating, and a host of smaller disturbances that combine to make a heck of a racket - from the shooter's perspective. Because your cheek is on the stock, these sounds are transmitted to you through the bones of your face. An observer standing five feet away hears less than half the noise the shooter hears. SO - to dramatically lower the noise of a spring rifle, tune the powerplant to remove as much of the clattering vibration as possible. One day I will post an article about how this is done.
I may not have answered the real question dsw was asking today, which is how to reduce the sound of a pneumatic or CO2 gun. I've danced around it by talking about barrel lengths and pressure levels, but I suspect he wanted something more. If that's the case, I'll be here to answer the next question.