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YouTube: VIDEO: LegallyArmedAmerica: Mass-produced factory ammo increasingly inconsistent

July 16, 2013

YouTube: VIDEO: LegallyArmedAmerica: Mass-produced factory ammo increasingly inconsistent

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{ 2 comments… read them below or add one }

JasonC July 16, 2013 at 8:34 am

The result is entirely misleading.

First, plus or minus doesn’t mean what you think it means, nor does variance mean highest minus lowest.

Second, the outlier you threw away was a much bigger deal with the handloads than the factory outlier was.

The actual mean and standard deviation of your hand loads was 989 +/- 6.8 FPS.
The actual mean and standard deviation of your factory loads was 1046 +/- 7.1 FPS.

The 6.8 SD for the first is 0.00689 of the mean, and the 7.1 SD of the second is 0.00677 of its higher mean. (It is higher simply because it is a lighter bullet).

Those are practically the same normalized standard deviation, and the factory one actually comes out as 98.26% of the hand load figure.

Small sample sizes and the dropped outlier don’t allow very much to be concluded from those tests, but the raw evidence before your picked outlier dropping procedure, and using the correct math, does not support your conclusion.

Note that it is a legitimate statistical procedure to drop the highest and lowest outlier from each set if both sets are large enough – around 20 say – and if you specify that procedure before conducting the firing tests. But to choose to drop the worst and only the worst outlier, from a very small sample, *after* you have seen one large outlier in the hand loads, is a biased procedure and statistically unsound.

FWIW.

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shaun July 16, 2013 at 2:52 pm

I’d be pissed if I opened a box of factory ammo with bullets seated that deep. There is no excuse for that other than poor quality control.

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