This is an extract of an article that might be interesting to some of us.
''Just as there are basic elements to correctly aiming a rifle or operating a lathe, – there are basic techniques required to draw meaningful conclusions from experiments with a chronograph. These techniques come from statistics and require only a simple calculator to check.
So what have we learned and how do I pick a good load?
• The more data you include in a calculation, the more statistically accurate it will be. So with respect to component choices, start with the same components the winners are shooting. There is far more data in all the rounds they fire collectively with good results than you can possibly collect on your chronograph. If it works for them, it will work for you.
• Start about 10% below maximum charges and work your way up to the desired velocity in small powder increments using 5 shot groups checking for pressure signs as you go. The goal is to get up to the desired velocity and the theory has shown that reasonably accurate estimates can be obtained with these small sample sizes.
• Testing for velocity variations requires larger sample sizes – 5 shot samples will not yield reliable results. For my rifle, 20 shot samples showing a standard deviation between 7 and 13 would seem to be an achievable standard based upon the current analysis and would suggest that the true population standard deviation was near 10 ft/sec.
• New combinations should be tested with 20 shots and should be considered an improvement only if the sample SD is below 7. Even then it could be a lucky group and should not be considered a true improvement until firing a second 20 shot string with SD below 9 confirms the performance.
• Similarly, new combinations tested with 20 shot strings should not be considered inferior unless the sample SD is greater than 13. 20 shot strings resulting in a SD between 7 and 13 have an 80% chance of equaling the performance of our 10 ft/sec population benchmark.
Following these basic guidelines, you can use your chronograph to develop long range loads similar in capability to those used by the nations finest shooters. I believe that you will find that by making statistically sound judgments, many loads produce statistically similar results and loads in general are not as finicky as current conventional wisdom would lead us to believe. Time with the chronograph is best spent confirming you do not have a bad load rather than spent searching for the magic combination. In reality, your shooting performance will probably improve since you can spend more time practicing with your set load and less time playing around with load combinations that have little or no statistical significance in terms of shooting performance. Finally, an additional caveat: the true measure of the accuracy potential of a load should be measured not on the chronograph but on the target paper at the intended full range. However, when evaluating group sizes, please remember to use sufficient samples to draw a statistically valid conclusion… ''
The whole article can be viewed at:
http://riflemansjournal.blogspot.ca/2010/07/statistics-for-rifle-shooters.html
''Just as there are basic elements to correctly aiming a rifle or operating a lathe, – there are basic techniques required to draw meaningful conclusions from experiments with a chronograph. These techniques come from statistics and require only a simple calculator to check.
So what have we learned and how do I pick a good load?
• The more data you include in a calculation, the more statistically accurate it will be. So with respect to component choices, start with the same components the winners are shooting. There is far more data in all the rounds they fire collectively with good results than you can possibly collect on your chronograph. If it works for them, it will work for you.
• Start about 10% below maximum charges and work your way up to the desired velocity in small powder increments using 5 shot groups checking for pressure signs as you go. The goal is to get up to the desired velocity and the theory has shown that reasonably accurate estimates can be obtained with these small sample sizes.
• Testing for velocity variations requires larger sample sizes – 5 shot samples will not yield reliable results. For my rifle, 20 shot samples showing a standard deviation between 7 and 13 would seem to be an achievable standard based upon the current analysis and would suggest that the true population standard deviation was near 10 ft/sec.
• New combinations should be tested with 20 shots and should be considered an improvement only if the sample SD is below 7. Even then it could be a lucky group and should not be considered a true improvement until firing a second 20 shot string with SD below 9 confirms the performance.
• Similarly, new combinations tested with 20 shot strings should not be considered inferior unless the sample SD is greater than 13. 20 shot strings resulting in a SD between 7 and 13 have an 80% chance of equaling the performance of our 10 ft/sec population benchmark.
Following these basic guidelines, you can use your chronograph to develop long range loads similar in capability to those used by the nations finest shooters. I believe that you will find that by making statistically sound judgments, many loads produce statistically similar results and loads in general are not as finicky as current conventional wisdom would lead us to believe. Time with the chronograph is best spent confirming you do not have a bad load rather than spent searching for the magic combination. In reality, your shooting performance will probably improve since you can spend more time practicing with your set load and less time playing around with load combinations that have little or no statistical significance in terms of shooting performance. Finally, an additional caveat: the true measure of the accuracy potential of a load should be measured not on the chronograph but on the target paper at the intended full range. However, when evaluating group sizes, please remember to use sufficient samples to draw a statistically valid conclusion… ''
The whole article can be viewed at:
http://riflemansjournal.blogspot.ca/2010/07/statistics-for-rifle-shooters.html
