Chronographs, ES/SD and Accuracy – What’s Myth and Reality

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grauhanen

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Many shooters use chronographs. Most shooters look at ES/SD. And a lot of shooters may be drawing conclusions the data cannot support.

This is not for shooters who don’t want to use chronographs. It’s not a call for shooters to use them.

This thread is about separating what chronographs actually tell you from what shooters may think they tell you. It’s about helping guide shooters wishing to use chronographs to avoid common misunderstandings and about clearing up some common chrony myths.

I will be making a number of posts here. If you can, please wait until I finish.
 
I will use real data that’s been acquired first hand. I shot about 20000 rounds of Lapua Midas in 2024 - 2025 and chronographed all of them.

• I used multiple rifles
• nine lots of Midas +
• targets based on ten-shot groups at 100 yards
• Garmin Xero C1 chronograph
• pencil and paper and calculator

If you’ve ever wondered whether ES?SD predicts accuracy, whether you can rank lots by chronograph, or whether different rifles get different chrony numbers, this thread will answer those questions with evidence, not folklore.

We will look at some of the most common ideas about chronographs and rimfire.

• ES/SD and predicting accuracy
• Chronographs identifying the lots that will perform best
• ES/SD performance is rifle-dependent
 
The “technical” terminology – MV, ES/SD

First let’s make sure that common chrony terms are understood the same way. Nothing yet about actual performance on target.

Chronographs measure the muzzle velocity (MV) of each round close to the muzzle. They will identify the slowest and fastest rounds rounds in a string of shots. This is the extreme spread (ES). A smaller ES is usually more desirable than large one. Strings of many rounds more reliably reflect the MV characteristics of a certain batch or “lot” of ammo.

Standard deviation or SD is a measurement that most modern chronographs generate. SD measures MV patterns within a string. The number tells the shooter how alike those rounds are in MV.

Two strings of 30 or 50 shots can have the same ES, even the same average MV. But their SD can be quite different. The MV pattern between the fastest and slowest rounds may not be the same.

To use an analogy, think of kids on a school bus. ES tells you when the earliest and latest kids get off the bus. SD tells you how clustered they are, whether they are stepping off one after another or trickling out randomly. In other words, are they getting off all around the same time, or are they leaving one at a time, less predictably?
 
Overview of ES/SD Characteristics Between Lots

In general ES/SD figures are not the same throughout any variety of .22LR match ammo, including Lapua Midas, the variety tested here. This means ES/SD varies between lots of the same ammo.

 
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Overview of ES/SD Characteristics Within Lots

Most .22LR shooters are aware that there are differences between lots. Lots of one particular variety may look identical but they may behave differently. For example some lots are faster or slower.

It’s important to understand that within a lot all is not the same in chrony terms. ES/SD varies. It’s not the same from one box to the next. How much ES/SD varies is lot-dependent. Some lots are more stable in terms of ES/SD variation, some less stable.

The crucial point is that all lots will have a range of ES/SD. Many shooters may be surpised by how much ES/SD varies within lots. Below are examples from the ammo I tested that give an idea of ES/SD variation within the lot.



This chart shows the rifles that shot with this lot. It shows the number of boxes each rifle used. It also shows the average ES of all boxes and the average SD. What’s worth noting here is that not all boxes are the same. The chart shows the lowest ES and SD per box for each rifle and the same for SD.

This was a more stable lot of Midas ammo. Below is one that’s less stable. The ES/SD varies much more. Low ES and SD in the 20s and low 5s, respectively. On the high side we see ES figures for some boxes a little over 50 fps and double digit SDs.

 
Now we can get into a most important part.

Chronographs and Accuracy Performance

A lot of shooters get chronographs with the aim of using them to predict accuracy.

Unfortunately it’s a myth that ES/SD predicts accuracy.

The general thinking, especially among many newer .22LR shooters, is that “Low ES/SD means small grous. High ES/SD means large groups.”

Through no fault of their own, a lot of shooters and chrony users intuitively believe there’s a consistent and verifiable relationship between ammo velocity and and how consistent it is and what happens on targets downrange. It seems rational, seems to make sense.

Wind aside, it’s intuitive to accept that a round’s velocity will determine it’s POI (point of impact). Faster and slower rounds will naturally have vertical differences in POI due to gravity. If ten rounds in a group are very close to each other in MV they ought to have little vertical spread between them on target. This should result in a tighter, smaller group.
 
Reality: A chronograph measures velocity, not precision. Accuracy depnds on many variaples a chronograph cannot see. If ES/SD predicted accuracy, then:

• groups with the same ES would be the same size
• lots with low ES/SD would always shoot best (wind aside)
• lots with high ES/SD would always shoot worse (again, wind aside)

None of these things is true. More specifically, sometimes they happen to be true but they aren’t always true. “Sometimes” doesn’t make a rule.

Tight ES and low SD don’t guarantee how the ammo performs. This is true outdoors and in testing facilities.
 
Does ES predict POI – An example

Here’s a simple exaple that helps illustrate the inconsistent relationship between a round’s MV and POI. Below are two ten-shot groups at 100 yards. They were shot with the same lot of Midas, the same rifle, on the same day. Both ten-shot groups have virtually identical ES.



If ES explained group size, these two groups would match. They don’t.

This is not a one-off example. This happens regularly and is not unusual. It can be expected to happen. Why? MV (and ES/SD) don’t consistently predict were a round will impact. MV simply doesn’t consistently explain POI.

To repeat a point, low ES and low SD don’t guarantee how ammo will perform.
 
Let’s look at a little more chrony data about ES/SD.

Consider the chronograph data shown below. For each of the nine examples the ES/SD numbers for two boxes are shown. The boxes were from the same lot and shot consecutively with the same rifle.

The eleven examples show four different rifles shooting five different lots of Midas.




These boxes have higher than average ES and/or SD, averaging 36.8 and 7.1 fps, respectively. The average ES for all lots was 32.9 and average SD was 7.1 fps.

What kind of performance did this at best “ordinary” Midas ammo produce?
 
Is Ammo with Poor to Mediocre ES/SD Destined to do Poorly?

Below is a chart showing how the mediocre ammo actually performed.

Seven of the eleven examples produced 100 yard ten-shot group averages under 0.800". By most standards, that is very good for .22LR.

Four were between 0.800" and 0.850". That’s still very good. All were much better than the overall average of any lot.




Ordinary MV and SD numbers but still great accuracy.

ES/SD isn’t an accuracy destiny. It doesn’t guarantee where you are going.

Accuracy is not a simple function of ES/SD.
 
Lots with Good ES/SD are capable of producing great results.

It is not a stretch to say that lots with very good ES and SD averages are capable of producing great results. It’s important to keep in mind the the majority of .22LR match ammo produces a range of outcomes, all the more the further the target.

Ammo with poorer ES/SD can deliver excellent results. Similarly lots with good ES/SD can give mediocre results time and again.

To illustrate, two of the best lots I have tested are M715 and M682, both used exclusivly in 2024. Between them a total of 4700 rounds were thot with an overall weighted ten shot group average of 0.956". That’s pretty good for .22LR ten-shot groups at 100.

At the same time:

• only two ten-group averages were under 0.800"
• only seven more were between 0.800 and 0.850"

Everything esle was usually “very good” but not spectacular. These lots seem to have a tighter range of outcomes. Rarely especially good, not often especially poor. Always expect a range of outcomes.
 
Will a Chronograph Identify the Best Lots?

A common idea is that by comparing ES/SD between lots you can pic the best one.

Sometimes this may work out. But does it work as a consistent rule?

The best chrony numbers are not necessarily consistent with the best performance on target.

The first chart shows how the chronograph would rank the nine lots of Midas. The next one shows how the targets actually rank them.



Midas lot M311 ranked low by chrony values alone. By target evaluation, it's a very good lot. Very mediocre chrony numbers yet very good target results.

The conclusion is obvious. If chronograph numbers correctly ranked lots, this result would be impossible. But it happened.
 
Do Rifles change ES/SD?

Does ES/SD of a lotdepnd on the rifle doing the shooting? Will different rifles give very different ES/SD values with the same lot?

With limited testing it will be impossible to know. Since the same boxes of any ammo can only be tested once, those boxes cant be compared with different rifles. We know that different boxes from the same lot will have differences in ES/SD. It’s normal and expected.

With large samples its’ possible to determine if ES/SD is rifle-dependent.

Below are charts showing different lots tested and ES/SD variation by rifle.



 
There are differences between rifles, but they are generally small:

• SD differences of about 1-3 fps
• ES differences of about 5-15 fps

But the important point is this:

The rifle influences ES/SD slightly. The ammo determines it overwhelmingly.
 
What Chronographs are Actually Good For

Chronographs can be useful – just not for predicting accuracy.

The are excellent for:

• establishing a rifle’s MV
• tracking MV with temperature (warmer temps = faster MV; cooler temps = slower MV)
• detecting rounds with unusual MV behaviour
• monitoring MV consistency

A chronograph is like a thermometer. It tells you when something is normal or not – but it cannot tell you how well a lot will shoot. It tells you whether you’re hot or not. It doesn’t tell you why.
 
Closing Thoughts

If you’ve gotten this far, here’s the bottom line:

Chronographs are valuable tools – but they are velocity tools, not accuracy tools.

Your targets will always tell you more about a lot than your ES/SD ever will. Across rifles, across lots, across thousands of rounds, the pattern is consistent.

• ES/SD does not predict accuracy
• Chronograph numbers do not rank lots
• Rifles do not meaningfully change ES/SD
• Good ammo is good across good barrels
• Bad ammo is bad everywhere (no barrel “fixes” bad ammo)
• Targets are the only accuracy instrument

If you want to understand how a lot shoots, you must shoot it. If you want to understand how a lot behaves, a chronograph can help – as long as you don’t expect it to do something it can't do.

Velocity is not precision. ES/SD is not accruacy. Chronographs measure speed. Targets measure truth.
 
grauhanen said:
What Chronographs are Actually Good For

Chronographs can be useful – just not for predicting accuracy.

The are excellent for:

• establishing a rifle’s MV
• tracking MV with temperature (warmer temps = faster MV; cooler temps = slower MV)
• detecting rounds with unusual MV behaviour
• monitoring MV consistency

A chronograph is like a thermometer. It tells you when something is normal or not – but it cannot tell you how well a lot will shoot. It tells you whether you’re hot or not. It doesn’t tell you why.
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I agree!

I have yet to go down this rabbit hole.

I don't have any experience, but I suspect, as with all measuring instruments, calebration and repeatability can be an issue.

I wonder how much variation there would be with same rifle, same chronograph, similar temperature and pressure, two weeks apart?

I think it would be interesting to see just how repeatable results may be.

Likewise, if two units (different or similar) are used at the same time, how comparable are the results one to another?
 
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