Barrel Harmonics 101
Part 1: Good Vibes Only – Vibrations, Carbon Fiber Sleeves, Barrel Tension and Barrel Tuners
Whether it’s somebody’s auntie sending “good vibrations” on Facebook, TikTokers talking about “the Vibe”, or airgunners writing forum posts about barrel tuners, optimizing vibrations seems to be all the rage nowadays.
This blog would probably have many, many more readers if it was dedicated to aligning oneself to higher vibratory planes instead of airguns, but c’est la vie.
“Barrel harmonics” has become one of the hottest topics in the airgun industry.
There has been an influx of products meant to “improve” harmonics in the hopes of achieving greater precision. Carbon fiber sleeves, barrel tensioning systems, and several different harmonic tuners have been released to the market. Rimfire and centerfire shooters have been using products similar to these for years, but these are new developments for the airgun industry.
There is a lot to be said about taming or tuning barrel harmonics. It can be a complicated subject for the uninitiated. This will be the first in a multi-post series dedicated to explaining barrel harmonics. This post will explain precisely what we are talking about when it comes to harmonics in a beginner-friendly way. Part 2 will be a detailed breakdown of installing a carbon fiber sleeve and post-installation precision test to see if there is any benefit to be gained. Part 3 will be all about harmonic tuners and testing some of the principles I will explain in this blog post.
There is significant crossover between airguns and firearms. The theory and principles involved are largely the same.
Harmonics = Vibrations
As soon as the trigger is pulled, a chain reaction begins. Tripping the sear sends the hammer barreling towards the valve and upon striking it, air rushes up the transfer port and forces our projectile down the barrel.
All of these events create their own vibrations. All of these vibrations constructively interfere with, or amplify each other as they travel throughout the rifle. These vibrations move throughout the action, stock, and unfortunately for us, the barrel. The cumulative effect(s) of these vibrations is what we refer to as “harmonics”.
Many of these vibrations are dampened by the giant piece of squishy meat (e.g., the shooter) holding the airgun. Just as many vibrations, however, are not dampened and “ring out” as they travel through the rifle, and, more specifically, the barrel. These vibrations create microscopic movements at the muzzle and actually cause the muzzle to move very slightly. Below you will find a very popular illustration demonstrating what this looks like (although it is greatly exaggerated).
These vibrations create several nodes (“normal” barrel position) and anti-nodes (the crests and troughs). In other words, we can effectively model this vibration as a standing wave.
We would be incredibly fortunate if our muzzle only moved in two-dimensions. It vibrates three- dimensionally and the pattern of this three-dimensional muzzle movement will undoubtedly vary from rifle to rifle. Some may have an elliptical pattern with the inflection points oriented at 12 and 6, 3 and 9, or 2 and 8 o’clock. Some unfortunate souls may find they have a rifle that has teardrop shape muzzle vibrations.
Here is just an example of how many different patterns could manifest – the assumes an elliptical vibration pattern.
How Harmonics Affect “Accuracy”
We must remember that not only is our barrel moving due to these vibrations, but the pellet is also traveling down the barrel at the same time. This creates the potential for the pellet to exit the muzzle while it is oriented in different directions since the pellet does not travel at the same speed from shot to shot.
Let’s say, for instance, that at 880 FPS, the pellet exits the barrel at its “normal position” on the graph, but the same pellet moving slightly faster at 890 FPS exits on the barrel’s upswing while the muzzle position is slightly lower than its “normal” position.
This creates point of impact shifts. A harmonically “happy” gun is one where the barrel position will be in roughly the same spot despite variations in velocity. Since velocity is a key factor here, there be a scenario where a very consistent tune at the velocity we are looking for (i.e. 890 FPS with an extreme spread of 15 and a standard deviation of 4) will not yield the greatest precision if harmonically we are not situated at a point where the muzzle is in the same approximate location.
Calling this movement tiny would be an understatement, but our target is often 50, 100, or 200 yards away so even minuscule movements in muzzle position can have very discernible impacts.
Tuning and Mitigation
Assuming we do not want to change the velocity of our tune, the market has come up with several ways to deal with this phenomenon. Here is a brief explanation of a few of the more popular ones.
1. Barrel Tuners
The idea behind a barrel tuner is simple. Add a weight to the end of your barrel, and adjusting the weight or the position of the weight will change how the barrel vibrates. Shoot a bunch of different groups and leave the barrel tuner in the position that produces the tightest groups.
The FX Airguns Barrel Tuner (below), threads onto the muzzle. Turning the weight will move it back and forth allowing the shooter to find the optimal position. Adding, removing or repositioning barrel bands can also function effectively as barrel tuners, changing how the barrel vibrates.
Carbon Fiber Sleeves and Barrel Tensioning
Instead of trying to find the optimal harmonic node or anti-node, we can just try to decrease the total movement of the muzzle instead. This is the point of carbon fiber sleeving and tensioning.
Adding a carbon fiber sleeve makes the barrel stiffer, meaning that it will vibrate less. The concept is similar to a bull barrel. More mass and effective diameter means less vibration. This means that the anti-nodes (crests and troughs) are not only closer to the original barrel position but the frequency of the vibrations is also decreased so there is less muzzle movement overall.
This is my carbon fiber sleeved Air Arms S510. Notice the difference in diameter between the carbon fiber sleeve and the muzzle.
Barrel tensioning systems accomplish much of the same. Threading the shroud onto the muzzle of the barrel (as is done with many of the FX airgun designs) means that adding spacers where the shroud contacts the breech stretches the barrel. Again, this is undetectable to the naked eye, but it is similar to tuning a guitar. Tightening the string lowers the pitch, i.e., decreased wave amplitude (distance between nodes and anti-nodes), and the frequency.
The red line represents a standard barrel with no tension or sleeving. The blue line is a sleeved and/or tensioned barrel. Notice that not only is the movement less, but it is slower as well.
This entire post has been theoretical. None of this matters if these real world implements don’t do anything. That will be the subject of the next two posts. We’ll get down to business and see if all this fancy-shmancy stuff is worth the time, money, and effort.