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Harmonics in Shotgun Barrels

by Clark Bush

Harmonics in Shotgun Barrels

Vibrations. They affect our lives. Our speech is accomplished in part due to the vibrations of our vocal cords. Musical instruments produce sound in part due to vibrations and we are able to hear the speech of others and the beautiful sounds of musical instruments due in part to the vibrations of our ear drums.

Vibrations affect many parts of our lives and if you are a shooter, they may affect your ability to hit a target with your firearm, more than you might realize. The vibrations or harmonics of rifle barrels for example have been widely studied and discussed for many years.

With the advent of high speed photography, those effects were documented on film and we were able to see the whip like action produced in the barrel as a bullet made its way from chamber to muzzle. Many different methods and devices have been employed to reduce or control the effect of harmonics on rifle barrels.

My questions were, do the same harmonics that affect rifle barrels also affect shotgun barrels? If so, in what way did they affect them and could those harmonics be regulated in some way, similar to the way harmonics are regulated in rifle barrels to enhance patterns?

In my search for information, I could come up with no studies of the effects of harmonics on shotgun barrels. Was that because no work on harmonics in shotgun barrels had been done or if it had been done, were the results so inconclusive that nothing had been published?

Although I had nothing to support my theory, it appeared to me that if the performance of a rifle barrel could be improved by dampening or regulating the harmonics, the same could be true of shotgun barrels. The only way to learn if my theory was correct was to experiment with some available means of dampening vibrations and recording the results.

Toward that end, over the last few years, I have worked with shotguns and vibration dampeners in an effort to determine how, if at all, shotgun barrels are affected by harmonics.

I began by purchasing several "Sharpshooter X-Rings" (X-Ring) produced by Sims Vibration Laboratory http://www.limbsaver.com/, perhaps best known for their Limbsaver recoil pads. The X-Ring was designed to “dampen barrel whip” on rifle barrels.

I experimented with the X-Ring using a plain barreled Savage shotgun. To determine if the X-Ring would have any effect at all on the shotgun barrel, I fired that gun 5 times with the standard unaltered barrel to create a baseline for performance.

Next I cleaned the bore and following the instructions for "free floating barrels", installed the X-Ring "3/4" from the end of the barrel" and fired 5 rounds.

I cleaned the bore again, and this time folloiwing the instructions for "supported barrels", installed the X-Ring "3/4" from the foreend" and fired 5 more rounds.

I cleaned the bore again and installed the X-Ring to a position 1/2 the length of the barrel from the chamber to the muzzle and fired 5 more rounds. (There were no instructions to do this but I wanted to see if a somewhat random position had any effect on the barrel.)

After each battery of tests, I located the most dense 3" core pattern and drew a circle around it. Then I drew a 10" circle around the balance of the pattern around that core. In that manner I could determine the point of impact (POI) and compare it with the point of aim (POA) of each shot fired.

I noted that there were changes in the (POI) and (POA) with each battery of tests. Every time I moved the X-Ring, the POI changed and those changes in POI differed from the unaltered barrel.

I had fired each shot from a stable rest, used the same brand and lot number of shells, allowed the barrel to cool between shots and the atmospheric conditions were the same for each battery of tests. Since the POI moved when I changed the postion of the X-Ring, I concluded that the barrel was affected in some manner.

I found these initial results interesting and they seemed to support my theory that a shotgun barrel, like a rifle barrel was affected by dampening its harmonics. I documented and cataloged all of these results. I spent some time reviewing them and evaluating their implications.

While at the NRA Convention in Pittsburgh, in 2011, I overheard two men engaged in a conversation about the effects of harmonics on rifle barrels.. They were at the Teludyne Tech Industries booth. You can read more about this company by visiting their web site at http://www.teludynetech.com/

The short story on this company is that they have developed a product, the StraightJacket Barrel System, that demonstrably improves rifle barrel performance. One part of that improvement is by increasing the rigidity of the barrel and reducing vibrations (harmonics) of the barrel.

I made arrangements to visit Teludyne in Greer, South Carolina and learn more about their product.

About 2 months later I visited Teludyne and after a discussion with their engineers, I had the StraightJacket Barrel Systems installed on the Savage barrel that I'd used in my earlier tests.

This was a first for Teludyne. They had only installed the StraightJacket on rifle barrels previously. Neither their engineers nor I knew what results to expect but if it affected rifle barrels by increasing rigidity and decreasing the harmonics of those barrels, my theory was that it would do the same for my shotgun barrrel.

I had data on the unaltered Savage shotgun barrel as well as data on the barrel with the X-Ring installed in various locations. Now I would need to return to the range to see how or if the StraightJacket system affected the performance.

This was a major step in my evaluation process. The StraightJacket system is a permanent installation and it would no longer allow me to experiment with the X-Ring on the barrel due to its increased diameter. I would however be able to compare the density of pattterns before and after the installation of the StraightJacket.

I fired 5 rounds and performed the same procedure that I had in the past of locating the most dense 3" patten and the surrounding 10" pattern to determine the POI. This time I also evaluated the 3" and 10" patterns for density and compared them to my previous results.

I found that all patterns, those with the X-Ring and those with the StraightJacket, had more pellets in them and that all patterns had fewer gaps than with the unaltered barrel. The StraightJacket equipped barrel also demonstrated more dense patterns than those of the X-Ring equipped barrel.

To this point, for this part of my study, I had fired all shots using a flush-mounted full choke tube, like the ones that come with most shotguns. I had not wanted to introduce any new variable that might skew the results. I had only been interested in what if any effect dampening the harmonics of a barrel might have.

That part of work with this shotgun was completed and now I wanted to see how the addition of an extended turkey choke would affect performance.

I repeated my original procedure and fired 5 rounds with an extended turkey choke installed. My examination showed that the 10" patterns were much more even and the number of pellets that the gun put into the 3” core were frequently doubled from the best that I'd seen in my previous evaluations.

It did not double the number every time and I still saw some inconsistency in the density of the patterns. I attributed that to the differences in performance of one shotshell over another. Having competed in still target shooting for over a decade, I have seen differences in performance from shell to another frequently.

When I considered the effect of the now more stable barrel, along with the evidence of the better patterns that it produced, I theorized that the inconsistences that I was witnessing could be caused in part not just by some inconsistency in the shotshells but by the fact that while the barrel was now more stable, the choke tube extending from the muzzle had in no way become more stabilized.

Therefore, perhaps the most important portion of the barrel, the muzzle end, the choke tube in this case, was still subject to those same harmonics that I'd been dealing with previously in the barrel. That led me back to the X-Ring.

From my earlier tests with the Savage barrel, I knew that the X-Ring influenced the point of impact. That caused me to theorize that it was dampening the harmonics of the barrel and that if it could dampen the harmonics of the barrel it might be able to dampen the harmonics of an extended choke tube.

The next test was to install the X-Ring on the extended choke tube to determine if my theory was correct.

To make that determination, it was necessaary for me to fire the gun with the StraightJacket equipped barrel and record the results without the X-Ring installed and then fire an equal number of shells, under the same or similar conditions with the X-Ring installed, record those results and compare them.

I fired 5 rounds without the X-Ring installed, cleaned the gun, then fired 5 rounds with the X-Ring installed. Results were quite different. While my StraightJacket equipped gun shot excellent patterns, the patterns were more dense and even by about 30%, with the X-Ring installed on the choke tube.

All this work had been done at my range which is at about 400' above sea level. I wanted to test this gun with and without the X-Ring installed in various parts of the country, at different altitudes and under different atmospheric conditions. Since I compete in still target shooting events http://www.nwtf.org/special_events/stilltarget/what_is_still_target.html from early March through late November of each year and travel over the east, midwest and southeast, that provided an excellent vehicle for my further testing.

These competitive events would serve as a real-world test for the performance of the StraightJacket alone and the StraightJacket and X-Ring combination and allow an additional 8 months for evaluation.

Competition in various locations could also test and verify, or nullify, in the presence of disinterested witnesses, the results I'd seen at my range. It was very important to support my conclusions and I could think of no better way to do that than by using the still target competition. Some of these events take place over 2 days and some are 1 day events. I divided the time equally when I had the X-Ring installed and when I did not and kept records of those results.

The results that I recorded in 8 months of competition with and without the X-Ring installed supported my previous experiences. Patterns were tighter, more dense and more even with the X-Ring installed than without it, by about the same percentage that I'd experienced previously, regardless of altitude or atmospheric conditions. I had no way to allow for differences in performance of individual shotshells and relied upon an equal number being fired with and without the X-Ring as my control.

I had fired the same Savage shotgun, with the original unaltered barrel, with the X-Ring alone installed, with the StraightJacket Shooting System installed and lastly with the addition of the X-Ring on the extended choke tube. I was able to track all of those results, compare them and determine that each step improved the patterning ability of the gun. Since both products were designed to reduce the harmonic effect of rifle barrels, I was able to conclude that they also had the same effect on shotgun barrels.

My conclusion was that dampening the harmonics in the barrel alone was very beneficial but that alone did not maximize the potential of the shot patterns. To accomplish that, it was necessary to dampen the harmonics of the extended choke tube. I accomplished that with the addition of the X-Ring.

Since many hunters and shooters might choose not to have the StraightJacket system installed on their favorite shotgun barrel, I chose to test the effectiveness of the X-Ring alone. In this series of tests I used a Mossberg 930 shotgun.

I copied my earlier procedure in every way, first firing 5 rounds without the X-Ring and then after cleaning the bore, firing 5 rounds with the X-Ring installed on the extended turkey choke tube. I did this using the same lot of shells and in one sitting to keep conditions as close as possible in each battery of tests. I also utilized the same procedure for evaluating the patterns and comparing POA and POI that I'd used with the unaltered Savage barrel.

I noted that the POI changed when the X-Ring was installed on the extended turkey choke. Based upon my earlier observations I interpreted this to mean that some change in harmonics had taken place even though the contact with the X-Ring was with the turkey choke alone.

I examined all of the targets with and without the X-Ring installed and found that there was an approximate 15% increase in pellet count and a pronounced improvement in the evenness of the patterns.

This test also allowed me to determine that dampeniing the harmonics on 2 different guns yielded very similar results. It also showed evidence that dampening the harmonics of the extended choke tube, either in conjunction with dampening the harmonics of the barrel or alone, influenced the POI as well as the quality of the pattern density.

What are the practical applications of this study and who is likely to benefit most from the information?

The first group that would seem to benefit would be those shooters who use a shotgun more like a rifle, turkey hunters. Turkey hunters aim their guns like rifles, many times use "dot" type sights or telescopic sights on them and use very tight chokes that concentrate the shot pattern. They are looking for dense and even patterns at distances up to 40 yards. They commonly evaluate their patterns using that previously mentioned 10" circle at that distance.

Will other shotgunners, hunters and clays shooters benefit from dampening the harmonics in their guns? Since my evaluations all produced results that showed an improvement in the quality and evenness of patterns, it would appear that any hunter or clays sport shooter would benefit from dampening the harmonics of his barrel or his extended choke tube.

The real challenge that I faced in writing this article was to make it concise enough so that a reader with at least a casual interest might take the time to read it and give the text some thought. It would have been fairly easy for me to get really caught-up in numbers and percentages which might put many readers to sleep long before giving up on reading the entire text. I also understand that there may not be enough information contained within the article for a reader with more than a casual interest in the subject. For that reason, I intend to publish a more detailed account of my work and make that available to those interested in learning more about this work, at a later date.

 

 

 

 

 

For more information, please visit this article's web page.
This article was published on Tuesday 08 January, 2013.
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