This post is by way of an introduction to the topic. When someone of Bryan Litz's stature does testing on something like rimfire barrel tuners, it's worth taking a look. There's not much published about it that originates with professional ballisticians or similar "experts". My own opinions are not expressed in this post. I'm just sharing information.
In the fall or early winter of 2022, Bryan Litz published his latest book, Modern Advancements In Long Range Shoooting, Volume III, published by Applied Ballistics LLC, 2022. It has a full chapter called "Barrel Tuner Testing".
What does Litz say? The "article" below is not real, but the contents convey the essential findings of Litz's rimfire tuner testing. The words attributed to Bryan Litz are in fact his own.

As noted above, Litz's words in the "article" come from the "tuner chapter" in the new book. The chapter is from pages 57 to 108 and includes discussion and analysis of barrel tuner testing on rimfire and centerfire rifles. The focus here is on the rimfire tuner testing.
What did Litz do and how did he test?
The Litz Applied Ballistics team tested a CZ 457 that has a Bartlein 1:12" twist barrel and a match chamber. The tuner was an ATS Hunting/Competition tuner.
Below, from page 60, are the details on the equipment used.

The following is a brief description of the testing.
To establish a control baseline, the rifle was first tested without the tuner. Testing with the tuner was done systematically, with a sweep of groups shot at "course" settings of 1/2 a tuner turn. The "best" and "worst" results were identified and retested. Repeated testing showed that the "best" and "worst" tuner settings did not continue to be the "best" and "worst". In fact, in some testing, the setting that produced the worst group in the intitial sweep ended up producing a better group than produced by the best setting in that initial sweep.
No doubt these kinds of results were frustrating for the testing team. They discussed the matter with the tuner manufacturer who thought the testing with settings of 1/2 a turn were too course to find an optimal setting. The team followed the advice to test at smaller increments, a "fine" sweep through the tuner settings.
Prior to the fine sweep testing, a new control baseline set of groups was shot without the tuner. This time the control baseline had better results than were intitially achieved. This was thought to be possibly due to the shooter "had refined some elements of how the gun was being shot" but in the end the reason was undetermined.
The fine sweep testing at smaller increments produced similar results as the course sweep testing. In other words, initial tuner settings that produced good or bad results could not be repeated with further testing.
Regarding Litz's conclusions about the rimfire barrel tuner testing, below are the salient points from page 72.

To summarize, Litz's team shot some 800 rounds through what should be a good rifle. They did not find any tuner setting that made a difference to the precision of the rifle. Regardless of setting, they found no evidence that the tuner made a difference. The testing results with the tuner remained impossible to repeat. Intitial testing that produced good results at certain settings didn't produce good results later. Similarly, settings that were supposed to be "bad" could later produce very good results. In short, there were no tuner results that were reliably repeatable.
In the second post in this thread, some questions arising from the Litz information are posed. Please keep in mind that the Litz information is Litz's information. I'm not saying yet what I make of the Litz testing. I apologize if I've made errors above.
In the fall or early winter of 2022, Bryan Litz published his latest book, Modern Advancements In Long Range Shoooting, Volume III, published by Applied Ballistics LLC, 2022. It has a full chapter called "Barrel Tuner Testing".
What does Litz say? The "article" below is not real, but the contents convey the essential findings of Litz's rimfire tuner testing. The words attributed to Bryan Litz are in fact his own.

As noted above, Litz's words in the "article" come from the "tuner chapter" in the new book. The chapter is from pages 57 to 108 and includes discussion and analysis of barrel tuner testing on rimfire and centerfire rifles. The focus here is on the rimfire tuner testing.
What did Litz do and how did he test?
The Litz Applied Ballistics team tested a CZ 457 that has a Bartlein 1:12" twist barrel and a match chamber. The tuner was an ATS Hunting/Competition tuner.
Below, from page 60, are the details on the equipment used.

The following is a brief description of the testing.
To establish a control baseline, the rifle was first tested without the tuner. Testing with the tuner was done systematically, with a sweep of groups shot at "course" settings of 1/2 a tuner turn. The "best" and "worst" results were identified and retested. Repeated testing showed that the "best" and "worst" tuner settings did not continue to be the "best" and "worst". In fact, in some testing, the setting that produced the worst group in the intitial sweep ended up producing a better group than produced by the best setting in that initial sweep.
No doubt these kinds of results were frustrating for the testing team. They discussed the matter with the tuner manufacturer who thought the testing with settings of 1/2 a turn were too course to find an optimal setting. The team followed the advice to test at smaller increments, a "fine" sweep through the tuner settings.
Prior to the fine sweep testing, a new control baseline set of groups was shot without the tuner. This time the control baseline had better results than were intitially achieved. This was thought to be possibly due to the shooter "had refined some elements of how the gun was being shot" but in the end the reason was undetermined.
The fine sweep testing at smaller increments produced similar results as the course sweep testing. In other words, initial tuner settings that produced good or bad results could not be repeated with further testing.
Regarding Litz's conclusions about the rimfire barrel tuner testing, below are the salient points from page 72.

To summarize, Litz's team shot some 800 rounds through what should be a good rifle. They did not find any tuner setting that made a difference to the precision of the rifle. Regardless of setting, they found no evidence that the tuner made a difference. The testing results with the tuner remained impossible to repeat. Intitial testing that produced good results at certain settings didn't produce good results later. Similarly, settings that were supposed to be "bad" could later produce very good results. In short, there were no tuner results that were reliably repeatable.
In the second post in this thread, some questions arising from the Litz information are posed. Please keep in mind that the Litz information is Litz's information. I'm not saying yet what I make of the Litz testing. I apologize if I've made errors above.
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