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Factors Affecting ES


RickT

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I chrono'ed identical loads for both Bayou 124gr TCG and Bayou 124gr RN, the former a 1.06" and the latter at 1.14", in our 9mm 1911s.  I was surprised that the RN ES was 1/2 that of the TCG bullet.  I'll probably stick with the RN as I transition to using up my ton of WSF powder, but can someone recommend a good reference that discusses the factors?  These are subsonic rounds in the vicinity of 900 fps using mixed brass. 

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Have you done the measurements to see how much of each bullet is in the case? One may just be a smidge closer to the sweet spot of internal pressure than the other.

 

When doing ladder testing I’ve found there’s usually 2 charges with tight SD (and by default ES), and these loads are almost always the tightest shooting.

 

Sent from my iPhone using Tapatalk

 

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You really do have to do ladder testing to find the best loads.  You also have to try different bullets.  When I chrono, the minimum string is 10 rounds.  I very often do 20 round strings, because it is more exacting.

 

To get good SDs, everything has to fall into line.  Your powder must measure accurately, you must operate your press in a consistent manner,  and you must use good, consistent bullets, crimped with the same force.  You should easily achieve single digit SDs with a 9mm, but they won't be with bunny fart loads.

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Don't make too much of differences in extreme spread. Some powders have widely ranging extreme spreads from one string to another, while some powders are more consistent.

 

Extreme spread, and standard deviation, do not appear to be correlated with accuracy for the typical handgun at typical handgun distances. Sure, there are examples where there is a positive correlation, but there are examples where there is a negative correlation, and even more examples where is there no correlation.

 

Here is an article that looks at accuracy and standard deviation and extreme spread:  https://americanhandgunner.com/exclusive-consistent-velocity-accuracy/

Edited by superdude
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While superdude is correct about the potential accuracy, that is not why you want good SDs.  The lower the SD, the less over minimum PF you have to be.  For example, my Limited loads chrono out with SDs in the 4.x to 6.x range.  With loads that consistent, I can run 170 PF and even the slowest round still makes major.  If my SDs were in the double digits, I'd have to load hotter to have enough margin.

 

BTW, I have found that when SDs are single digits, long range accuracy is really good (I use good bullets).

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15 hours ago, zzt said:

You should easily achieve single digit SDs with a 9mm, but they won't be with bunny fart loads.

 

This. You’re currently shooting 111 PF. As an experiment, load up some 130ish PF loads and shoot 20 rounds of each over the chrono and shoot them both for groups.

 

There’s a point below which you inherently be inconsistent with any power: for example titegroup behind a 147 @ 120ish PF is beyond filthy and always had a high SD in my experience. Bring the load up to midrange in the book, and both of those things improve sharply.

 

Also echoing the sentiment that anything less than 10 rounds is statistically irrelevant for SD/ES purposes: particularly if you don’t consider your data carefully. Were all of them spread over 100fps? Or did you have 9 close ones and one round 97 FPS slow because some powder slopped out of that case or the bullet was cast a few grains heavier than most of them, or had a defect in the coating.

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On 11/8/2017 at 4:09 PM, superdude said:

Don't make too much of differences in extreme spread. Some powders have widely ranging extreme spreads from one string to another, while some powders are more consistent.

 

Extreme spread, and standard deviation, do not appear to be correlated with accuracy for the typical handgun at typical handgun distances. Sure, there are examples where there is a positive correlation, but there are examples where there is a negative correlation, and even more examples where is there no correlation.

 

Here is an article that looks at accuracy and standard deviation and extreme spread:  https://americanhandgunner.com/exclusive-consistent-velocity-accuracy/

That's an excellent article.  For those of us who shoot steel challenge low velocity, high ES can be the norm.  Of course the gun must cycle; thank goodness 1911s are easy to tune for light loads.  I suspect there is a velocity below which the projectile won't stabilize which would dramatically affect accuracy, but I haven't seen that sort of issue running 124gr coated lead at 900fps +_40 fps.  These are heavy, steel guns so recoil management is pretty easy, but lower recoil is IMO better especially for use super seniors..

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On 11/8/2017 at 6:09 PM, superdude said:

Don't make too much of differences in extreme spread. Some powders have widely ranging extreme spreads from one string to another, while some powders are more consistent.

 

Extreme spread, and standard deviation, do not appear to be correlated with accuracy for the typical handgun at typical handgun distances. Sure, there are examples where there is a positive correlation, but there are examples where there is a negative correlation, and even more examples where is there no correlation.

 

Here is an article that looks at accuracy and standard deviation and extreme spread:  https://americanhandgunner.com/exclusive-consistent-velocity-accuracy/


Thanks for this article.  I've been pretty focused on keeping low SD/ES in my loads for the past year or so, and Prima SV in 40 has really fit the bill for those numbers.  Much to my surprise though, a recent test run I did of N320 powder, which had about 3x higher SD/ES than the Prima SV load, seemed to consistently produce groups about half the size.  That seemed a bit counter-intuitive to me, but as soon as I saw it, I knew it might be time to start doing more "real world" testing after making sure I hit PF, rather than fretting about the numbers...

Edited by fbzero
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