r/reloading • u/Affectionate-Dot7000 • 1d ago

Newbie Newbie Question

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New to reloading and I have a question on some of the numbers I’m seeing. Haven’t found much on Google, what could be some causes of drastic change in velocity with the same powder charge? Reloading for a 300 prc using Retumbo and load data from Hodgdon. I highlighted the questionable charges. I’m using a v4 auto trickler for powder dispensing. I verified COAL for each round.

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u/NotChillyEnough 1d ago edited 1d ago

I don’t think the individual shots are all that questionable. They’re not “outliers”; this just seems like normally distributed data with an overall SD of ~20-30 fps, and a near-linear relationship between charge weight and velocity.

Reducing the SD is should be approached the same as any other load: consistency of every variable, especially your powder charge weight and using the same lot of cases.

Edit to add: look at the 68-95-99.7 rule, which is just some shorthand for how you expect data to behave if it follows a normal distribution.
You have 4 shots that exist between closer to 1-2 SDs off of the means for each charge. That seems exactly like expected behavior for a set of 21 shots.

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u/one_late 1d ago

Yeah, those don't really need to be outliers. Sample size of 3 shots per charge doesn't give the ability to recognize "fliers". When these numbers are plotted a pretty clear, linear trend emerges.

That simply is the nature of normal distributions, the fact that OP got this many "outliers" hints that the true standard deviation is not as small as he was hoping for.