What “Causes” a Low SD/ES?

backwoodsshooter

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Question: what causes a low SD/ES?

I was going through notes and .3 grains made a difference of a SD3 ES7 to a SD12 ES20. How can a slight different in powder charge level create that change?
 

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General RE LEE

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Consistency in the overall reloading process.

Ive got a system down where I anneal, full length resize, bump shoulder back and trim each case and then I weigh every load. I load in batches of 15-20 and shoot recreationally at the range out to 750 yards. I learned years ago from a competitive black powder shooter that the reloading process of a black powder gun should be exactly the same everytime.
 

FEENIX

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Ive got a system down where I anneal, full length resize, bump shoulder back and trim each case and then I weigh every load. I load in batches of 15-20 and shoot recreationally at the range out to 750 yards. I learned years ago from a competitive black powder shooter that the reloading process of a black powder gun should be exactly the same everytime.
So "if" you got the "consistency in the overall reloading process" system down, why are you asking the factors affecting SD and ES? You seem to be contradicting yourself.

Question: what causes a low SD/ES?

I was going through notes and .3 grains made a difference of a SD3 ES7 to a SD12 ES20. How can a slight different in powder charge level create that change?

An inconsistency resulted from SD=3 and ES=7 to SD=12 and ES=20, i.e., inconsistencies in powder charges between load configuration.
 
Last edited:

MagnumManiac

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It all boils down to start pressure. A uniform start pressure equals a curve under MAP that is consistent. A start pressure that fluctuates causes variation in MAP…this is where ES/SD numbers vary causing poor numbers.
There are numerous ways this can be influenced or changed; crimping, seating depth, neck tension and even primer type.
Poor ignition is to be avoided at all costs.

Cheers.
 
Last edited:

nksmfamjp

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When you say you have it “down”, I think:
What is the accuracy of your tools/process?
What is your process design?
How did you determine primer type, bullet, powder, neck tension, case fit, case brand, etc?
What are the measured results: predictive like runout or charge variation? Also, final results like group size, sd, mean radius?
Also when you post an sd/es…..how many rounds in the chrono group? By definition, when the sample accurately predicts the population, ES>= 6xSd for a normal distribution.

ob_5d0980_20191201-103230-1.jpg
 
Last edited:

FEENIX

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Great Falls, MT
When you say you have it “down”, I think:
What is the accuracy of your tools/process?
What is your process design?
How did you determine primer type, bullet, powder, neck tension, case fit, case brand, etc?
What are the measured results: predictive like runout or charge variation? Also, final results like group size, sd, mean radius?
Also when you post an sd/es…..how many rounds in the chrono group? By definition, when the sample accurately predicts the population, ES>= 6xSd for a normal distribution.

ob_5d0980_20191201-103230-1.jpg

L😇L! Now you've done it...
 

RYEWSKY25284

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When you say you have it “down”, I think:
What is the accuracy of your tools/process?
What is your process design?
How did you determine primer type, bullet, powder, neck tension, case fit, case brand, etc?
What are the measured results: predictive like runout or charge variation? Also, final results like group size, sd, mean radius?
Also when you post an sd/es…..how many rounds in the chrono group? By definition, when the sample accurately predicts the population, ES>= 6xSd for a normal distribution.

ob_5d0980_20191201-103230-1.jpg
Genius.
 

SFMongo

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san antonio
QA (Quality Assurance) QC (Quality Control). QA same weight, size, and uniformity of your brass and bullets. Quality Control: Accurate and uniformity in loading plus shooting i.e. barrel temperature. Even if you did all this you have no control over your powder quality. Guess what at the end of the day there are two things that will minimize SD just like about everything else in this world. Time and Money. LOL
 

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