What is your target ES/SD

[Shadow9mm]

So I have never been able to get a straight answer on this question. I have heard everything from single digits, to it does not matter. For those that do care about it, I can never seems to get a straight answer as to what they consider to be acceptable, what is bad, or what their target goal it.

While watching this video today, the creator stated that match ammo is supposed to have a SD of 15 or less. Right around the 6min mark.

https://www.youtube.com/watch?v=LsK2i1aMpVE

Is this correct? What are your target goals or what do you consider acceptable/unacceptable if your willing to share. are there any official military standards?

[tangolima]

SD in fps alone is meaningless to me. I like the ratio CV=SD/mean better, or coefficient of variation. My target is below 0.5%.

For example, 5.56 going at 3000fps. I want to keep SD below 15fps. 9mm going at 900fps, SD below 5fps.

Enough number of samples is also important. At least 10, better 30.

ES has even less meaning. I always try to estimate the corresponding SD using equations suggested by unclenick.

-TL

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[Nathan]

To me, Sd from 10+ shots is very important.

For pistol loads, it doesn’t matter much, but over 30 would be weird.

For AR15 loads, over 25 would be excessive.

For hunting loads, including long range-ish, over 15 is too much. IME, factory match ammo runs 20-25.

For real long range, I like under 10ish.

This said, I don’t panic about it as 20 probably won’t take me out of a good shot at deer at 600 yards.

3 shot and 5 shot sd’’s are cute, but pretty meaningless.

Saw a guy at the local range talking 5 shot Sd’s in single digits. I smirked. Then his buddy caught him deleting a shot. Even they thought he was crazy!

[Shadow9mm]

I typically to 10 shots, however now that I have my garmin and can chrono while I shoot groups that number is going in increase significantly.

[74A95]

The question is, why/when does it matter? The argument for vertical stringing seems to apply to very long ranges for rifles, like 500+ yards, but of course this will depend on how large the ES/SD is.

For pistols, ES/SD does not correlate with group size at a typical handgun distance of 25 yards.

[Jim Watson]

No, but it is still a measure of consistency.
My PhD friend got into reloading and considered a CoV of 1% or less to be “match grade”.

And consider that if you are shooting at long range where velocity variation causes elevation variation, you are not shooting the SD, you are shooting the ES. They all count.

[Nick_C_S]

It depends.

I usually do 10-round samples. Sometimes more. Last time out, I was testing some 38's, and I was doing 18-round samples; but, that's atypical.

In the handgun world, if it's a heavy bullet, using a fast propellant, such as a target wadcutter, I see SD's in the single digits, or slightly more (<15), on a frequent basis.

If it's a hotter round (think 357 Mag), under 20 is my goal, but under 30 is okay too - especially if it's a light bullet with slow propellant.

In the rifle world, I only load/shoot 223 Rem through an AR platform. My 55 and 65 grain rounds typically have SD's in the 20's, touching 30's. If it's a No.41 primer, nearly double that.

I did load some 75gn Hornady's for the novelty of it (BTHP's 1:7 twist) and their SD's were excellent - in the teens, and <10.

[Metal god]

I did a test a long time ago now that showed how you hold the firearm significantly impacts SD/ES . The short version is interacting with the rifle the least amount possible results in the lowest standard deviation and extreme spread . Meaning the tighter you hold the rifle and harder you pull it into your shoulder. The worst those numbers will be. I posted those results here on the forum in real time like eight or 10 years ago. I was at the range and posting the numbers as I shot. I don’t know if I can find the thread after 7000 posts but I’ll give it a try

Edit : I can’t find it. It must be buried in somebody else’s thread or I’m not sure what I titled it , Who knows why

Point being is You wanna test those numbers in the conditions the rifle will be used . If it’s a benchrest rifle, you should be testing it from your rest. If it’s a hunting rifle, you should be holding it in your hands pulled tight into your shoulder. This will give you your true standard deviation and extreme spreads in the conditions you intend to use the firearm.

All that said I’ve only cared about my standard deviation and extreme spread in rifles with muzzle velocity from 2600 to 3000 ft./s . In those cases I like low teens. It’s pretty hard to get into the single digits in my opinion but I have done it .

[FrankenMauser]

I want single digits.
But for most rifle loads, an ES of 40 is not too bad.

For handguns, it doesn't matter. I shake too much for an ES or SD of 100+ to really make a difference.

[Nathan]

CoV

What is this?



FIGURED IT OUT

Originally Posted by ChatGPT

CoV typically stands for Coefficient of Variation in the context of reloading, ballistics, and accuracy testing.

What is CoV?
• Mathematically:
CoV = (Standard Deviation / Mean) × 100
It’s usually expressed as a percentage.

In Reloading/Accuracy Context:
• CoV is often used to measure consistency in:
• Velocity (FPS)
• Group size
• Powder charge
• A lower CoV means more consistency, which usually translates to better accuracy and precision.

Example (Velocity CoV):

Let’s say you fired 5 rounds and got:
• Mean velocity: 2700 fps
• Standard deviation: 12 fps
Then:
CoV = (12 / 2700) × 100 = 0.44%

That’s a very low CoV and indicates a highly consistent load.

[stagpanther]

Meaning the tighter you hold the rifle and harder you pull it into your shoulder. The worst those numbers will be.

You got me on that one--I don't understand the correlation between the two.

[mehavey]

Inconsistencies in physically holding the rifle does have an effect on the mv=MV games...
so I can understand that.

On the other hand, not securely holding a hard-recoiling rifle -- is going to play havoc
with both group size & impact point.

"SD" is small potatoes at that point.

[Nathan]

Huh. My CoV for my load I’m freaking out about is 0.6%! Maybe it’s ok??

Sd = 19, MV = 2930 fps, CoV = 0.6%

GTG? My typical GTG value is under Sd < 15.

[stagpanther]

Inconsistencies in physically holding the rifle does have an effect on the mv=MV games...
so I can understand that.

On the other hand, not securely holding a hard-recoiling rifle -- is going to play havoc
with both group size & impact point.

"SD" is small potatoes at that point.

Inconsistencies--yes I get that. Maybe I misunderstand the way it was written--seems to me to say the tighter you hold and/or pull in the worse the numbers get. That's the part I don't get.

BTW--since you're likely the only other person on the forum who might be interested --I'm currently working up some fast 115 gr ext penatrator loads for my 350 legend AR. I downloaded load suggestions from Hodgdon but QL tells me they are way over max so I'm starting significantly below their loads. I think QK is right, my start loads were not far off from the velocities it projected. I'm a bit nervous since the last time I got "adventurous" with my 350 legend AR it ended up blowing up on me.

[mehavey]

I looked at the Hodgdon site, but don't have that exact 115gr Lehigh bullet they listed.
But every other similar bullet/shape I tried at max loads still came up high 50's-mid 60's.

Bad juju.....

[stagpanther]

The one they list I believe is for controlled chaos--but dimensionally it's the same as the penetrator though probably a bit better BC. But being a solid copper you have to factor in higher start pressures.

[Metal god]

My test involved me doing two different things . Pulling the rifle in tight and keeping a death grip on it . And the other was to let it freely recoil with me only pulling the trigger and keeping the rifle from flying off the table . The freely recoiling shots had single digit SD. The shots with me holding the rifle tight had double to triple that SD . I did not test for accuracy in that test. I didn’t even care where the bullets were going other than over my chronograph rather than through my chronograph haha .

Both tests were done on the same day relatively close together with the same rifle and the same load just letting it cool down between Tests

[tangolima]

Metal. Do you recall the rifle and bullet weight? Did you notice change in mean velocity when you shouldered the gun differently? You measured the speed with optical chrono or labradar?

-TL

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[Unclenick]

The idea behind covariance is to make SD the same portion of velocity at all velocities. But that begs the question: What does that tell you about vertical dispersion? If I run ballistic tables with the same bullet at different starting velocities, I soon find that the amount of vertical dispersion I get from a given covariance is lower at higher velocities. For example, with a 90-grain Berger .224 VLD, if I fire it at 3000 fps, I can allow a 1.4 times larger covariance than I can firing it at 2600 fps and still get the same vertical dispersion at 1000 yards from both loads.

Well, I say "get", but that isn't always exactly so, either. All the ballistics software assumes firing from a perfectly rigid gun. A real gun's muzzle doesn't hold perfectly still, and the difference in barrel time could nullify that 1.4 times ratio or enhance it by changing at what phase in muzzle deflection (aka "vibration") the barrel is in when the bullet exits.

The bottom line is, you've got to test what you have to see what that actually is.

[stagpanther]

My test involved me doing two different things . Pulling the rifle in tight and keeping a death grip on it . And the other was to let it freely recoil with me only pulling the trigger and keeping the rifle from flying off the table . The freely recoiling shots had single digit SD. The shots with me holding the rifle tight had double to triple that SD . I did not test for accuracy in that test. I didn’t even care where the bullets were going other than over my chronograph rather than through my chronograph haha .

Both tests were done on the same day relatively close together with the same rifle and the same load just letting it cool down between Tests

Hmmm...still a mystery to me--though I guess it's cosmically possible that allowing the rifle to jump maybe it allows the bullet to "evade" the initial pressure wave riding in front of the muzzle as the bullet exits?? That's beyond my pay grade and would need a response from better minds than mine like JohnSka, DavidSOG or Unclenick.

[mehavey]

Most bench rest types use free-recoiling set-ups so mv=MV is precisely repeatable on the rifle side.
Understandable.

But for real world (even varmint worlds) one is holding the stock into the shoulder to some consistent
degree even if free-resting everything else on a forearm bag.

[stagpanther]

MV is precisely repeatable on the rifle side.

That I get--it could be any technique as long as it's consisently repeatable--in other words you could theoretically toss it into the air twirling like a cheerleaders baton and as long as it discharged at precisely the same position you'd still get smaller ES/EDs.

[tangolima]

Energy diverted to recoil is determined by the ratio of bullet mass (weight) to rifle mass. In a pretty extreme scenario of heavy 200gr bullet fired from a light 5lb rifle, only 0.5% of the total energy goes to recoil, lowering MV by 0.25%.

Leaning into the butt stock increases the effective mass of the rifle, arguably. The argument is there is always compressible material between the stock and shooter's bone. It has delay effect. By the time the shooter's body mass shows up in the picture, the bullet is long gone. For argument sake, let's say the rifle is solidly bolted to a wall, and no recoil is possible, MV will increase by no more than 0.25%. The load needs to have similar CV for this to be observable.

I'm afraid what Metal measured is due to something else.

-TL

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[JohnKSa]

I wonder if pulling the rifle really tight to the shoulder could reduce the compressibility aspect enough to start to bring body mass into the picture.

[Shadow9mm]

Originally Posted by JohnKSa

I wonder if pulling the rifle really tight to the shoulder could reduce the compressibility aspect enough to start to bring body mass into the picture.

Perhaps, based on the amount of energy generated, and the mass of the gun, only so much can be effectively transferred during the firing process. Like trying to pour 8oz of water into a 6oz cup. But when you combine masses, holding it tight, more energy can be transferred, or it can be transferred more easily as it is going into aluminum larger mass. Kind of like reducing a bottle neck or choke point?