There have been quite a few articles written regarding barrel harmonics, locally and aboard. I found one particular article very interesting where the author talks about two main points:
1. Most barrels vibrate in an elliptical pattern as they travel on the X & Y axis, but mainly they vibrate in the vertical plane (Y axis).
2. Ideally, you want the pellet to exit the barrel at the point where the barrel is almost at its highest peak.
You would think that this would be the worst possible case, as the barrel is the furthest from its position of rest. In fact, the barrel is coming to rest at that moment, because it is changing direction and has very little movement in the X & Y axis.
I once tested the accuracy of a certain barrel and found that the barrel shot great groupings at 800 and 1000 fps. Anything between was poor. In effect, when I was adjusting the air rifle velocity, I was altering the timing of when the pellet exits the barrel in its vibration cycle.
I started to wonder if there could be a way to alter the frequency at which a barrel vibrates, so one could shoot a certain pellet weight at a set velocity (900 fps) and achieve great accuracy.
In my quest for greater accuracy, 100 m metallic silhouette shooting, I embarked on a project to build a silencer that I could DIAL in the accuracy to the best combination my barrel, pellet and velocity would allow.
The prototype BFT silencer I built allowed me to make adjustments by using the weight of the silencer to alter the barrel vibrations. My goodness, this silencer was super sensitive!. It y took only a few degrees of adjustment and would send the POI marching all over the target. (See photo below)
The photo below is a typical grouping of my unregulated P12 & 4.5 mm HW100 barrel with JSB Beast pellets shooting in a strong gusting wind at 75 m blowing from left to right. The point of aim is the end of the white diamond.
The photo below is BFT Silencer first range outing and was shot directly after shooting the grouping above. The same windy condition, distance and air rifle set up, the pellet to the right must have been a damaged pellet that I did not notice before shooting it.
The first thing I noticed was that the BFT silencer converted a horizontal shot grouping to a vertical shot grouping and MAN it really works!. I also realised that the prototype BFT silencer had to be redesigned to be less sensitive to adjustment.
Due to work commitments and time restraints I shelved this project for a year.