Doom2
Well-Known Member
Assuming you are shooting your groups at 100yds your groups are NOT affected by velocity to a detectable level. A 100 fps variation in MV from 3000 fps is within ~0.1". You would have to be an expert shooter with an unbelievable rifle to detect this. What gives good groups at 100yds is repeatability in the muzzle line of sight alignment with the target and repeatable alignment of the bullet centerline with with the muzzle line of sight.
Looking at and comparing standard deviation based on a 5 shot sample is running a fools errand. To have confidence that a 10 SD is actually less than a 17 SD would require 12 shots for each group when using standard statistical methods. The standard deviation 95% confidence interval on a 5 shot group with a 10 SD is 5.99 to 28.74 fps. What that means is that if the true standard deviation is 10 then 95% of an infinite number of 5 shot groups would have SDs fall between those values.
A chronograph measures velocity. It knows nothing of direction of the bullet. Most of the significant contributors to velocity variation are due to brass preparation along with case capacity and powder fill. There are also some chamber related affects that can affect the entire combustion process (such as being in the lands versus just off).
IF you are happy this 3/4 MOA then you load is probably good enough. You may be able to improve the SD by working on consistency in case preparation and possible seating depth.
Looking at and comparing standard deviation based on a 5 shot sample is running a fools errand. To have confidence that a 10 SD is actually less than a 17 SD would require 12 shots for each group when using standard statistical methods. The standard deviation 95% confidence interval on a 5 shot group with a 10 SD is 5.99 to 28.74 fps. What that means is that if the true standard deviation is 10 then 95% of an infinite number of 5 shot groups would have SDs fall between those values.
A chronograph measures velocity. It knows nothing of direction of the bullet. Most of the significant contributors to velocity variation are due to brass preparation along with case capacity and powder fill. There are also some chamber related affects that can affect the entire combustion process (such as being in the lands versus just off).
IF you are happy this 3/4 MOA then you load is probably good enough. You may be able to improve the SD by working on consistency in case preparation and possible seating depth.
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