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Rifles, Reloading, Optics, Equipment
Reloading
Powder choice vs ES and SD
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<blockquote data-quote="Doom2" data-source="post: 2723008" data-attributes="member: 108323"><p>I don't know that any one powder is going to be intrinsically better than another but one of the main things that affects SD is the case fill. A case that is close to full is likely to have tighter SD than one less full so powder selection to get close to full is important. Conventional wisdom has been that single base extruded powders yielded smaller SD than spherical and ball powders. However that logic may not be the case today, or as significant a factor as it used to be.</p><p></p><p>Be careful when you go down the SD/ES rabbit hole. Many chase small standard deviations and look at small sample sizes. It is statistically unreliable to evaluate standard deviations with less than 20 samples. By definition the standard deviation does not fit a normal distribution like the mean (average). it is bounded by zero on the low side and it fits what is called a Chi-Squared distribution. To develop confidence in the standard deviation it takes a significant number of shots. When someone says they have a standard deviation of 8 fps that number has a confidence interval associated with it. For 3 shots that range is 4 to 50 fps. For 5 shots its 5 to 23 fps. For 10 shots 5.5 to 14.6, and for 20 shots it's 6 to 11.6 fps. If the reloader was looking for single digit standard deviation for his handholds he would be very unlikely to have it from the 3, 5, or even a 10 shot group. Even with the 20 shot group there is only a 75% confidence interval. This means that if an infinite number of 20 test were done 75% of them would be in the range of 6 to 10 fps.</p></blockquote><p></p>
[QUOTE="Doom2, post: 2723008, member: 108323"] I don't know that any one powder is going to be intrinsically better than another but one of the main things that affects SD is the case fill. A case that is close to full is likely to have tighter SD than one less full so powder selection to get close to full is important. Conventional wisdom has been that single base extruded powders yielded smaller SD than spherical and ball powders. However that logic may not be the case today, or as significant a factor as it used to be. Be careful when you go down the SD/ES rabbit hole. Many chase small standard deviations and look at small sample sizes. It is statistically unreliable to evaluate standard deviations with less than 20 samples. By definition the standard deviation does not fit a normal distribution like the mean (average). it is bounded by zero on the low side and it fits what is called a Chi-Squared distribution. To develop confidence in the standard deviation it takes a significant number of shots. When someone says they have a standard deviation of 8 fps that number has a confidence interval associated with it. For 3 shots that range is 4 to 50 fps. For 5 shots its 5 to 23 fps. For 10 shots 5.5 to 14.6, and for 20 shots it's 6 to 11.6 fps. If the reloader was looking for single digit standard deviation for his handholds he would be very unlikely to have it from the 3, 5, or even a 10 shot group. Even with the 20 shot group there is only a 75% confidence interval. This means that if an infinite number of 20 test were done 75% of them would be in the range of 6 to 10 fps. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Reloading
Powder choice vs ES and SD
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