Min, max, ES, Average and SD

[GetReal]

Question: Is it possible for a given single load, with a given (fixed) powder type, charge weight and bullet weight, to decrease extreme velocity spread and standard deviation, without changing powder / charge weight / bullet, etc? Say by seating depth? What are the things that most effect SD, ES and Avg?

Neck tension? Moly coating? Bbl fouling / cleaning? Other?

From time to time I get really accurate loads, even to 600 + yds, but not really stellar SD, ES, etc. My thinking is these loads will go wonky out past 6 - 800 yd.

Bonus Round: Is it true that bolt guns will most usually get better SD / ES that autoloaders / semi autos.?

Thanx.

 

[Beiruty]

1) Yes. If the powder is very consistent in its burning rate for the same lot and same container, it would show less SD and less ES of MV, than another unstable gunpowder. Also, temperature insensitive gunpowder such as H4350 would have very little MV rise if the outside temperature is rising.

2-5) Many factors. However, the most important factor for very consistent MV is good brass. That is very uniform and consistent in volume and construction.
6) In general, bolt-rifles are more accurate than SA due to their construction AND, all the gas behind the bullet is pushing the bullet until the bullet leaves the barrel. In SA, the gas directed for bolt-cycling could vary and, thus, the MV could vary too.

 

[GetReal]

2-5) Many factors. However, the most important factor for very consistent MV is good brass. That is very uniform and consistent in volume and construction.

Aaahhh, yes.... good reminder - brass prep. That's my next rabbit hole. Got my AMP annealer and getting ready to chase brass prep.

Anyone wanna point me to the main brass prep considerations, I'd be grateful.

 

[Beiruty]

 

[Ned Ludd]

One of the best ways to optimize the various velocity outputs is by testing different Lot#s and/or brands of primers. It is often possible to find one specific primer that generates better numbers than the others.

 

[GetReal]

One of the best ways to optimize the various velocity outputs is by testing different Lot#s and/or brands of primers. It is often possible to find one specific primer that generates better numbers than the others.

Good point. Forgot that too.

 

[xswanted]

Neck tension is so often overlooked when SD and ES are being discussed.

Assuming quality brass is being used I believe it to be a major factor in how a load performs.

 

[3Sigma]

First question is the one most here would love to solve. You can run a DoE on it with statistically significant sample sizes run in a controlled environment and let us know (you'll also burn up a barrel and a few thousand rounds). If you want quality ES and SD results, you need 8 to 10 samples per variable set.

Or, you can take the empirical approach most here follow and change the big things first, slowly progressing until your results are indistinguishable from.random noise. The left side of the pareto has been discussed here already.

 

[K22]

First let me establish that I have not spend a lot of time / effort / ammo on measuring velocity variations and seeking to reduce them via component changes and / or reloading procedure changes.

I don't even own a chronograph but have access to one via a shooting buddy. When I did venture into this world it was with the 22 250 seeking velocity data so that I could apply the data to more precisely determine bullet drop at extended distances using drop tables / data.

The one factor I discovered was that ball powder, while capable of exceptional accuracy, was quite susceptible to velocity variations with temperature changes and even small powder charge changes. However, I didn't notice any significant accuracy changes on paper. What I did experience was pressure surges in high temperatures, i.e., 90 degrees + in the field.

In theory, the smaller the velocity variation from round to round the greater the precision. This seems to be an empirical truth. While I have NOT done extensive testing and I'm not a bench rest or long range (> 300 yard) shooter, I found that chasing this velocity variation data to be of little value in achieving desired shots on target. By your own admission, you have achieved "really accurate loads with less than stellar ES and SD values".

So, why not let the target tell you how well a load is performing? Of course, you want to produce as consistent reloads as possible and only change one element at a time if you are not achieving the results that you want but why not let shots on target guide you rather than chasing ES and SD variation measurements. Aren't shots on target the ultimate indicator on load performance?

 

[Doom]

Question: Is it possible for a given single load, with a given (fixed) powder type, charge weight and bullet weight, to decrease extreme velocity spread and standard deviation, without changing powder / charge weight / bullet, etc? Say by seating depth? What are the things that most effect SD, ES and Avg?

Neck tension? Moly coating? Bbl fouling / cleaning? Other?

From time to time I get really accurate loads, even to 600 + yds, but not really stellar SD, ES, etc. My thinking is these loads will go wonky out past 6 - 800 yd.

Bonus Round: Is it true that bolt guns will most usually get better SD / ES that autoloaders / semi autos.?

Thanx.

Well, the first question is what do you considers "Stellar"? The second is what are you trying to accomplish. Are you trying to hit a target or generate low SD and ES? What is your target beyond 800yds and at what distance? What are you shooting, cartridge, bullet? What kind of groups do you shoot at 100yds (5 shot minimum)? Are you shooting quality brass or mixed brass? There are other things that affect accuracy/precision as much or more than SD. As for ES if you have a reasonable sample size it is meaningless as it only represents 2 of the rounds tested.

As others have noted, the primary contribution to low SD is consistency. That comes from quality, consistent components and uniform brass preparation and loading. It is extremely difficult to single out specific effects such as seating depth because of the uncertainties associated with testing. Some will say yes because the test results are different but that doesn't mean that the true values are different.

 

[Coyotefurharvester]

And equipment used for obtaining velocity readings, a .3%+- accuracy is an issue with sd. That's 21 fps possible error at 3500fps from the actual velocity.

 

[GetReal]

In theory, the smaller the velocity variation from round to round the greater the precision. This seems to be an empirical truth. While I have NOT done extensive testing and I'm not a bench rest or long range (> 300 yard) shooter, I found that chasing this velocity variation data to be of little value in achieving desired shots on target. By your own admission, you have achieved "really accurate loads with less than stellar ES and SD values".

So, why not let the target tell you how well a load is performing? Of course, you want to produce as consistent reloads as possible and only change one element at a time if you are not achieving the results that you want but why not let shots on target guide you rather than chasing ES and SD variation measurements. Aren't shots on target the ultimate indicator on load performance?

Perhaps I communcated poorly. The best groups I've gotten have always* had single digit SD's, and sub 20 FPS ES.... which I may be wrong, but theoretically and in my experience is the best indicators at 100yd of what will be a conistent load at 800 yd.

And yes.... the target tells the tale. Problem is I have a 400 yd max range I could post paper targets, and 2 bad knees that let me know it any time I walk more than 100 yds. Everythign lese I got is steel. And the steel hits pretty much maintain the half moa at 100 out to 700.

Sorry for any confusion. Hopng this clears up what I'm trying to figure out. I'm trying to get this new caliber / load to the ES / SD that's been succesful in the past.

 

[GetReal]

Well, the first question is what do you considers "Stellar"? The second is what are you trying to accomplish. Are you trying to hit a target or generate low SD and ES? What is your target beyond 800yds and at what distance?

[/QUOTE]
I may be wrong but I understand low SD / ES to be key to good groups at distance. I really don't care about ES / SD, other than in that context. You point is well made....if it shoots, it shoots, regardless of the statistical data. But if it doesn't shoot, I should start looking at whats causing velocity variation (among other things) ...esp. when 1 round is 10" + lower than another at 600 yd.

What are you shooting, cartridge, bullet? What kind of groups do you shoot at 100yds (5 shot minimum)? Are you shooting quality brass or mixed brass? There are other things that affect accuracy/precision as much or more than SD. As for ES if you have a reasonable sample size it is meaningless as it only represents 2 of the rounds tested.

Caliber: 6ARC
Bullet 105 Berger HT
Brass: 6.5 Nosler Grendel fire formed to 6 ARC
Current groups: ~ 0.75" at 100 yd (several 5 shot groups)
Rifle: Semi-auto 20" Bartlein bbl 1:7

To my limited* understanding, SDS / ES are kinda irrelevant...UNLESS your groups are opening up from 100 yd out to 800 yd. Then - again ...my understanding - I should look for what's causing ES / SD variations, as that's gonna affect bullet trajectory. Especially ES cuz if one out of 5 rounds is 35 fps slower than another, those 2 are gonna have very different trajectories at distance.

 

[Straightshooter1]

As others have noted, the primary contribution to low SD is consistency. That comes from quality, consistent components and uniform brass preparation and loading. It is extremely difficult to single out specific effects such as seating depth because of the uncertainties associated with testing. Some will say yes because the test results are different but that doesn't mean that the true values are different.

SD's and ES's only tells me about the consistency in my reloading and I only look on paper for how the load are actually performing since I don't find a direct correlation for what I see on paper verses the velocity SD's and ES's. . . unless there's a very large difference in SD's and ES's; like what happened to me this weekend.

Typically, I get SD's in the single digits and ES's in the mid teens for 5 shots and get pretty good results on paper when I've got my loads tuned well. I loaded up 50 rounds of a load that works well for me where my SD's are at 7.2 and ES's at 17 out of my .308. I decided to use SRP's in Lapua Palma cases since I have a lot more of them than the LRP's. I've done this kind of thing before and got similar results that need very little tweaking, but not bad as this time. This time my SD was 16.2 and ES was 43 and the group's ES was barely under .5", though the Mean Radius was .164" and the second group a little worse at just over .5". I only shot 15 of the 50 rounds and decided not to do shoot any more of them because of the SD and ES I got and will wait until I can figure out what to do with the rest of the cartridges. Obviously, the load worked before with the LRP's, but the chrono data is telling me it doesn't like this small primer load configuration. Since I don't want to pull them and I've loaded pretty long, I think I'll try seating this batch substantially lower and see what happens. ¯\_(ツ)_/¯

 

[Capt. Oblivious]

Neck tension and check your brass, mark the case/cases that gives you that "ES Flyer". I have seen cases that weigh and measure the same as every other case yet they just don't want to work with the others. Might just be how they were drawn or something.

Im not a real ES freak but a friend I help with his reloads are one and we spend allot of time this season trying to get his 22250 as low as we could. Last outing he shot 10 shots over a Labradar with a 9 shots reading 3320fps and only one shot going 3319fps. 66JLK, N540, Norma brass and Russian primers loaded on 21st century arbor press with Wilson DIES

His in AUS now for the next couple of weeks so I’m interested to see If we can come close to replicate this but I do believe neck tension and how you treat those necks are very important. One other thing we also changed out was changing to a 21st century hand priming tool that might also have something to do with it.

On my rifles I generally see ES around 15-18fps over 5 or so shots when I measure speed or If I look at electronic target feedback and they don't group to badly way past 600 yards. Be gentle with those necks, a little light brush with a nylon brush and some graphite applied to the inside of the neck before you drop your charge also doesn't hurt anything. I generally see better ES numbers going up in neck tension rather than going down, if you jam a bullet it doesn't really make a big difference but as your shooting a Semi id try adding a bit more neck tension

 

[Beiruty]

And equipment used for obtaining velocity readings, a .3%+- accuracy is an issue with sd. That's 21 fps possible error at 3500fps from the actual velocity.

It would not make a correctable difference until you cross 1000 yards and/or the target is minute.
Say, 8" target at 1000 yards.

 

[Beiruty]

 

[Beiruty]

full article

How Much Does SD Matter?

As long-range shooters, we tend to obsess over every little detail. After all, we’re trying to hit r...

precisionrifleblog.com

 

[CharlieNC]

full article

How Much Does SD Matter?

As long-range shooters, we tend to obsess over every little detail. After all, we’re trying to hit r...

precisionrifleblog.com

This completely ignores positive compensation, eg Audette ladder testing, which is the underlying principle most use when tuning a load.

 

[Beiruty]

This completely ignores positive compensation, eg Audette ladder testing, which is the underlying principle most use when tuning a load.

SD and ES has nothing to do with the following tune :"Barrel pointing down when MV is rising", however, with load SD/ES it would help stay in the "tuned node.
Regardless of lower SD/ES which correlates with vertical dispersion at very long range or increasing the MV to flatten the trajectory, or the actual tune, or even the group size itself.

At very long ranges. the wind would move the bullets in 10s of inches sideways when the wind call is off, or the wind is changing from mid to gusting each other minute.