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Re: Range Report - 8mm SLT - 5-28-15
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Old 06-01-2015, 02:29 PM
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Default Re: Range Report - 8mm SLT - 5-28-15

Here's my statistical analysis of the groups produced by shooting these two bullets. First the 220 Sierra bullets:


Then the swaged 136 grainers:


Of primary interest to me is the value for the Area of the 95% Confidence Ellipse seen in cell "F16". For the 3-shot 220 Sierra group, that value is 7.34 square inches; for the factory group it is about 101 square inches. For the 220 Sierra, that would be a rectangle about 2.25" wide by about 4" high. (Or more precisely, an ellipse with x-axis length of 2.26" by y-axis length of 4.14".) What that values predicts is the area into which I could expect the next 95 out of 100 shots to go at 100 yd. The combination of large group AND SMALL SAMPLE SIZE - only 3 shots - means that my 'confidence' in predicting where the next 95 out of 100 shots will go - BASED ON THIS SAMPLE - is very low.

If you look at cell "B3" you will see the value of "Student's t". That value is based on the sample size. The larger the sample size, the smaller the Student's t value. The Student's t value is a MULTIPLIER of the variance observed in the shot string. Therefore, the greater the number of shots you are using to determine the parameters (average, variance, etc.) the better the estimate of 'reality' you will have. Since the smaller the sample size the less confidence one has that the samples used actually REPRESENT REALITY, you have to broaden the PREDICTED parameter.

Taking "max spread" as an indicator of THE BOUNDARIES AROUND where the "next bullet" is going to hit is "optimistic" at best. Put another way, it's fooling yourself. There are PLENTY of people in the world that want to fool me, I don't need to fool myself. What I want to know is my BEST GUESS at where the 'next' bullet is going to hit based on where the last "X number" of them hit. Max spread is "easy", but it's not "good" for making that prediction/guess.

Paul

PS - If you have MicroSoft Excel and would like a copy of the spreadsheet so you could perform your own calculations, shoot me a PM and I'll email a copy with some instructions to you .

Paul
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Last edited by gitano; 06-01-2015 at 11:56 PM..
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8mm, 8mm slt, 8mm steyr, confidence ellipse, range report, statistics, swaged


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