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Required accuracy for powder charge

R

RetiredChief

Private
Minuteman
Mar 14, 2021
45
17
Newport News Va
#1
When you are working up a load to find the most accurate powder charge, What accuracy do you require? Also what delta do you use between loads. I use 0.2 grains (ie 40.0, 40.2, ect).

Listed accuracy for many of the digital powder scales is ± 0.1 grains so my powder charge could be as low as 39.96 grains, or as high as 40.04 grains. Is this accurate enough for load development?

Hove two digital scales, a Frankford Arsenal Platinum (± 0.1 grains) and a Gempro 250 (± 0.02 grains).

Both of these I have to what out for temperate drift. I normally leave on for 15-.30 min before use, maybe I should leave on longer.

I also have a 45 year old Beam Balance (Brand name “Texan” – LOL). Time consuming, but I can measure down to the ¼ -> ½ grain.
 
Last edited:
#2
RetiredChief said:
Listed accuracy for many of the digital powder scales is ± 0.1 grains so my powder charge could be as low as 39.6 grains, or as high as 40.4 grains.
Click to expand...

1628088779582.png
 
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#4
RetiredChief said:
When you are working up a load to find the most accurate powder charge, What accuracy do you require? Also what delta do you use between loads. I use 0.2 grains (ie 40.0, 40.2, ect).

Listed accuracy for many of the digital powder scales is ± 0.1 grains so my powder charge could be as low as 39.6 grains, or as high as 40.4 grains. Is this accurate enough for load development?

Hove two digital scales, a Frankford Arsenal Platinum (± 0.1 grains) and a Gempro 250 (± 0.02 grains).

Both of these I have to what out for temperate drift. I normally leave on for 15-.30 min before use, maybe I should leave on longer.

I also have a 45 year old Beam Balance (Brand name “Texan” – LOL). Time consuming, but I can measure down to the ¼ -> ½ grain.
Click to expand...
Your OP still shows uncorrected. Also your CW incremental granularity will be driven by your use case. For practical shooting, initial OCWs, I use .3 for most of my cartridges.
 
#7
RetiredChief said:
OPPs, I corrected it to read 39.96 grains, or as high as 40.04
THANKs
Click to expand...

If the scale's accuracy is ± 0.1 grains and your target is 40 grains, your range will be 39.9 - 40.1 grains

If the scale's accuracy is ± 0.02 grains and your target is 40 grains, your range will be 39.98 - 40.02 grains

It's just simple arithmetic.....
 
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#8
308pirate said:
If the scale's accuracy is ± 0.1 grains and your target is 40 grains, your range will be 39.9 - 40.1 grains

If the scale's accuracy is ± 0.02 grains and your target is 40 grains, your range will be 39.98 - 40.02 grains

It's just simple arithmetic.....
Click to expand...

You also have to consider linearity. All those scales promising .02gr accuracy are more than likely .08gr. To get true .02gr accuracy you need to step up to the next higher level.
 
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#9
918v said:
You also have to consider linearity. All those scales promising .02gr accuracy are more than likely .08gr. To get true .02gr accuracy you need to step up to the next higher level.
Click to expand...

I get it but I was just correcting the arithmetic errors, which boggles my mind.
 
#10
308pirate said:
If the scale's accuracy is ± 0.1 grains and your target is 40 grains, your range will be 39.9 - 40.1 grains

If the scale's accuracy is ± 0.02 grains and your target is 40 grains, your range will be 39.98 - 40.02 grains

It's just simple arithmetic.....
Click to expand...
Pardon My “Simple arithmetic” error. We Engineers do make typos occasionally.
  • Almost all digital equipment implied error is at best ± 1 LSD (Less significant digit). IE my $300 digital inclinometer accuracy is ± 0.05 degrees – 5 x LSD (0.01 Degrees)
  • When instrument (such as scales) states ± 0.1 grains that means that if it reads 39.9 to 40.1 grains for exactly 40.0 grains – it passes QA. This does not mean that (In the case of Power scales) that given powder charge can measure 39.9 to 40.1 grains (totally unexceptable).
  • If you “Calibrate” the scale with a 40.0 grain weight, and the scale is linear, then 39.5 would be displayed as 40.0 and 40.044 would be displayed as 40.0. Rounding rules. Meaning that your measurement could be ± 0.05 grains EVEN for a 100% accurate 0.1 grain meter.
Ignoring my poor math, Back to my basic question – would this be accurate enough then for Load development.
 
#11
I'm currently experimenting with loading on a progressive, CFE223 dropping it with the powder measure on the press... it's varying from 29.3 to 29.7-8 at a target of 29.5... still have single digit SDs... but I am in a wide node, with a cartridge that typically tolerates wide variance and is "easy to load"

if you have something like a 6x47L that is known as finicky, you may need tighter tolerance

at the end of the day, how much variance you can tolerate "depends" on your requirements, what powder you're using, and quite possibly what round you're loading for
 
#12
RetiredChief said:
Pardon My “Simple arithmetic” error. We Engineers do make typos occasionally.
  • Almost all digital equipment implied error is at best ± 1 LSD (Less significant digit). IE my $300 digital inclinometer accuracy is ± 0.05 degrees – 5 x LSD (0.01 Degrees)
  • When instrument (such as scales) states ± 0.1 grains that means that if it reads 39.9 to 40.1 grains for exactly 40.0 grains – it passes QA. This does not mean that (In the case of Power scales) that given powder charge can measure 39.9 to 40.1 grains (totally unexceptable).
  • If you “Calibrate” the scale with a 40.0 grain weight, and the scale is linear, then 39.5 would be displayed as 40.0 and 40.044 would be displayed as 40.0. Rounding rules. Meaning that your measurement could be ± 0.05 grains EVEN for a 100% accurate 0.1 grain meter.
Ignoring my poor math, Back to my basic question – would this be accurate enough then for Load development.
Click to expand...

You're mixing linearity, resolution, and accuracy into one mess. I'm not going to fix it.

You're overthinking this whole load development thing. Can't help you there either.
 
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#13
918v said:
You also have to consider linearity. All those scales promising .02gr accuracy are more than likely .08gr. To get true .02gr accuracy you need to step up to the next higher level.
Click to expand...
The GemPro 250 provides a calibration for linearity. Normal calibration is done at 0 g and at 20 g. To calibrate linearity, calibration is done at 3 points - 0g, 20g (supplied weight) and at 50 g (Not supplied). Myself, I verify three points A) zero B) 40, or 50 grains and C) 100 grains. If I pass these 3 points, I'm good to go - if Not I preform the 3 point calibration.
 
#17
He’s taking overthink to the next level

Two. Two threads, ha ha ha.

www.snipershide.com

Required accuracy of powder charge when developing loads.

When you are working up a load to find the most accurate powder charge, What accuracy do you require? Also what delta do you use between loads. I use 0.2 grains (ie 40.0, 40.2, ect). Listed accuracy for many of the digital powder scales is ± 0.1 grains so my powder charge could be as low as...
www.snipershide.com www.snipershide.com
 
#19
ill just ad to the mix of confusion lol

just because a scale has a certain spec there is a weight range in which that spec is accurate

example:
from 0-10 it might be .2
from 11-20 it might be .1
from 21-30 it might be .2
etc

for any scale you buy one needs to check the weight range they are accurate within

on our benches certain departments have 3 different scales even though they "overlap" in min/max capacity and resolution
 
#20
brianf said:
ill just ad to the mix of confusion lol

just because a scale has a certain spec there is a weight range in which that spec is accurate

example:
from 0-10 it might be .2
from 11-20 it might be .1
from 21-30 it might be .2
etc

for any scale you buy one needs to check the weight range they are accurate within

on our benches certain departments have 3 different scales even though they "overlap" in min/max capacity and resolution
Click to expand...
You are 100% correct.
For example low end digital Relative Humidity meters are typically inaccurate on the low end, MUCH more so than mid-range. Most of test equipment we used on satellite instruments are re-calibrated periodically and a calibration chare is included when returned, and if "Out-of-Tolerance" a FAILED sticker is applied.

This is the reason I use calibrated weights, close to the desired weight to verify the scale's accuracy, both at the beginning and periodically if weighing more than 20 minutes. For example, most of my charges are between 40 and 50 grains. So I check at 40 and 50 grains. If Both are off I do a simple Cal and recheck. If only one reading is off I then do a Linearity Calibration. NOTE: Calibration weights should only be handled with tweezers as you can transfer oil/moisture if using fingers, should be verified periodically.
 
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