When we develop an accurate rifle we make lots of choices: barrels, choice of bullets, primers, powders, loads, muzzle brakes, tuner, etc. How do you know when you have made a good choice? The purpose of this article is to provide a "scientific basis" for evaluating these choices with a minimum of shooting.
Anyone who has tuned an accurate rifle will understand how difficult it can be to find that best sweet spot. Typically, I will shoot two shots and turn the tuner a small amount and shoot two more shots. I continue this until I have obtained the smallest group. Frequently, the window for the best point of tune may only be a few degrees of rotation from another one that also looks pretty good. How do we tell which is the best tuner setting? The purpose of the Tuning With Confidence article is to provide a scientific basis for the decision making. Statistics have been used for process control and decision making for more than 75 years. Using these tools to make choices in accurate shooting is a logical conclusion. How do you know you have made the best choice?
Why two shots? The statistics for two shot groups measure the inherent variation of the rifle from shot to shot, this is what drives the size of larger groups. The group can never get smaller than the first two shots. What we are trying to measure is the change in group size with tuner setting. It is the number of groups shot (sample size) at a given tuner setting that is important not the number of shots in each group. Typically the group size of 3 shot, 5 shot and 10 shot will be progressively larger than the 2 shot group. Why shoot more shots than are necessary to measure change? Five 2 shot groups provide more data than one 10 shot group. We are measuring the change in one variable, i.e. the tuner setting.
Most shooters are familiar with concept of Average, Standard Deviation (Sigma) and Extreme Spread (E) from chronograph data. The concept of Confidence Interval (CI) is not typically used in evaluating data.
Standard Deviation is the measure of variability within the groups (samples) relative to the Average. Typically the Average +/- one Sigma means that 65% of the groups will fall in that range, Average +/- 3 Sigma would include 99.7% of the groups.
What Sigma does NOT tell us is how the Average will change. The Confidence Interval is the measure of change in the Average. The Average +/- CI is the measure of the change in the Average. We now have a Max Average and a Min Average.
What this means is that 65% of the groups will fall within the Max Average+ Sigma and Min Average-Sigma. With a large CI this can make a big difference.
I have been working with rifle tuning systems for almost 20 years and have fired thousands of rounds in the process. A better way to measure the results of changes was needed, CI proved a valuable tool. This concept can be used to evaluate any variables such as, barrels, powder charge, seating depth, primers or anything where measurement of change is wanted.
TUNERS WORK but they need to be adjusted properly to get the best results.
I hope this helps in better understanding the Tuning With Confidence article. You can contact me at PrecisionTuners@aol.com.
Jim Bennington
) and examine the results. Once I identify a promising region or regions, I'll re-test that particular zone, looking not only for small groups/spread/whatever, but also consistency with the original results that led me down that particular path. Most people simply 'average' the results and call it good; if my understanding of what is being advocated in this article is correct the author(s) are simply taking it up another level and trying to apply some math to predict how much that average is going to vary over the long run i.e. confidence interval. It's a more rigorous process than the back-of-a-napkin math that many people use (including myself), but thats not a bad thing. Maybe not everybody's cup o' tea, but to each their own.
