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Old May 22, 2020, 02:50 PM   #1
jetav8r
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Ever calculate the standard Deviation of your powder measure?

Today I decided to calculate the Standard Deviation of the powder measure on my Dillon 550B. The powder was BE-86 at 5.8 grains. I weight 10 drops on my electronic scale which measures to hundreds. The average was 5.76 and the SD was .0257. Wish I could SDs like that with my reloads.
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Old May 22, 2020, 03:07 PM   #2
hounddawg
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I have no idea what BE-86 is. Flake ? fine ball ? extruded ? I have never measured the SD of my throws but I can promise fine ball is going tpo have a smaller SD than say H4350.
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Old May 22, 2020, 03:36 PM   #3
berettaprofessor
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What's the gold standard? Beam scale? Not sure mine measures hundredths to be able to check.
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Old May 22, 2020, 05:04 PM   #4
hounddawg
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Just did my RCBS Chargemaster 1500. Threw 20 charges of IMR 8208 XBR which is a short stick ( extruded) at 30.2 gns, measured them on my A&D 120.

Avg 30.19
min 30.10
max 30.28
SD 0.05
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Old May 22, 2020, 06:00 PM   #5
44 AMP
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Quote:
Ever calculate the standard Deviation of your powder measure?
Nope.

First, because its going to be different with every different powder, and could be different with the same powder due to fill density.

Second, because I'm an old guy, with old equipment (my scale only does down to tenths) and if I feel the need for that degree of precision, I'm going to be weighing every charge, anyway.
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Old May 22, 2020, 07:24 PM   #6
higgite
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FWIW, I checked my Chargemaster 1500 way back when with IMR 8208 XBR and got these numbers:
20 drops w/ auto dispense set for 25.0 gr
Avg 24.98
Max 25.04
Min 24.9
SD 0.043

I also did my Dillon case activated measure on an RCBS Pro 2000 with W231:
Avg. 4.32
Max 4.42
Min 4.28
SD 0.034
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Old May 22, 2020, 07:52 PM   #7
LeverGunFan
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What is interesting in this exercise is that what we typically call a powder measure meters the powder by volume only, so we should expect some variation in weight due to variation in density and powder packing in the metering chamber. A device like the RCBS Chargemaster on the other hand meters the powder by weight, with no regard to volume, so we would think it would have less weight variation. The standard deviations measured here seem comparable, but the measure and the Chargemaster should be compared using the same powder, preferably from the same bottle. The measures probably perform better on small flake powders, and the Chargemaster less so on large extruded powders.
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Old May 22, 2020, 07:55 PM   #8
hounddawg
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this is a interesting thread, be interesting to see more tests
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Old May 22, 2020, 09:48 PM   #9
NoSecondBest
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Statistically speaking, you need to do a gage R&R study to evaluate the tool you're using to measure. Next, you need to calculate gage error. You need to calibrate the gage and check it for accuracy. And most importantly, you need to know what the end result means to the process. As a retired quality/statistical engineer and a long time shooter.....you're probably wasting a lot of time with this in the grand scheme of things related to accuracy gains.
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Old May 23, 2020, 10:46 AM   #10
Wag
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Originally Posted by NoSecondBest View Post
Statistically speaking, you need to do a gage R&R study to evaluate the tool you're using to measure. Next, you need to calculate gage error. You need to calibrate the gage and check it for accuracy. And most importantly, you need to know what the end result means to the process. As a retired quality/statistical engineer and a long time shooter.....you're probably wasting a lot of time with this in the grand scheme of things related to accuracy gains.
All of this. It's a nice curiosity, to be sure, but it would have zero effect on how I reload. Something else I've always noticed when reloading is through the duration of a long loading session, the powder measure will start to drift ever so slightly and after 1,000 rounds, the ending throws may be just a smidge more or less than at the beginning of the loading session. Difficult to know what variable can cause this but I think you need a lot more than 10 samples.

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