Group size evaluation

[WKR]

most barrel companies, custom or semi custom rifle builders, and even factory rifle manufacturers typically all have a 3 shot sub moa and in some cases sub half moa guarantee.

Now 3 shots isn't enough of a sample size to really collect data from. I know most consumers are not really dedicated shooters and believe that a 3 shot group is great for a hunting rifle.

When you extrapolate this with quantity of shots and group size, does the accepted standard then grow as the groups open up with the cone of fire?

for example
3 shot .5 moa
5 shot .8 moa
10 shot 1moa
And 30 shot plus or barrels cone 1.5 moa

Thats the data I'm interested in, not just a cherry picked 3 shot group. And I wish the manufacturers would put more effort into establishing what the true cone is.for their products, although I understand why this might not be feasible.

 

[Shortschaf]

does the accepted standard then grow as the groups open up with the cone of fire?

If this is the question, the answer is:
Yes, it should

You would need to change the point of view of the average consumer for manufacturers to start marketing differently

Group size guarentee holds almost as much water as MPG guarentee on a new vehicle. Its just marketing. It'll be close, but it's often worse than advertised

 

[Cactus kid]

Absolutely the accepted standard grows as the round count on groups gets larger. But you will notice the difference in multiple group sizes tends to be more consistent the more rounds are in a group.

Example:

If you look at five different 3 shot groups, one group might be 1", one group might be .25"

Take five different 10 shot groups, the diffence between the smallest and largest group is going to be minimal. Statistically, over 90% of rounds will fall into the cone of a 10 shot group.

 

[WKR]

Okay then Let's use Allterra's 3 shot .50 moa guarantee as an example.

I wonder how many of these rifles are actually a half moa gun. I would wager the true cone is probably double that. Yet the most of the consumers of those rifles will tell you they have a half moa rifle.

I guess what I'm trying to say is a sub moa guarantee from a manufacturer doesn't translate into a sub moa rifle. And 3 shot groups are statistically insignificant unless using multiples and comparing or overlaying them to create a larger sample.

 

[Formidilosus]

Okay then Let's use Allterra's 3 shot .50 moa guarantee as an example.

I wonder how many of these rifles are actually a half moa gun.

None, or virtually none- if you consider 95% probability to be the standard.

I would wager the true cone is probably double that. Yet the most of the consumers of those rifles will tell you they have a half moa rifle.

The true cone at least to a 95% standard is going to be closer to triple the “3 shot group” size.

I guess what I'm trying to say is a sub moa guarantee from a manufacturer doesn't translate into a sub moa rifle. And 3 shot groups are statistically insignificant unless using multiples and comparing or overlaying them to create a larger sample.

Correct. It’s marketing BS.

 

[Formidilosus]

When you extrapolate this with quantity of shots and group size, does the accepted standard then grow as the groups open up with the cone of fire?

for example
3 shot .5 moa
5 shot .8 moa
10 shot 1moa
And 30 shot plus or barrels cone 1.5 moa

That would only work out close to that if you shot a significant number of “groups” at each, and then used the overall averages. If you shoot a couple of 3 shot groups and picked one or two that were .5 moa, most likely you would end up with a 1.7-2.0 moa 30 shot group for a 95% confidence. The curve starts flattening out at around 20 shots, and by 30 shots it is very steady. Somewhere between 50-100 shots the cone just stops growing for all practical purposes.

Thats the data I'm interested in, not just a cherry picked 3 shot group. And I wish the manufacturers would put more effort into establishing what the true cone is.for their products, although I understand why this might not be feasible.

It’s feasible, they just don’t want to. First- manufactures aren’t shooting and testing like most believe they are. Second, the manufacturers don’t understand statistics and probability, nor are they shooters- they don’t know. Third, you’d have to educate the consumer in some way- because they are as ignorant as anyone.

A “30 shot Extreme spread sub 2moa” guarantee”- means a whole hell of a lot more than a “.25 moa 3 shot, cold bore, match ammo” guarantee. The first is real and provable, the second is window dressing nonsense.

 

[aschuler]

most barrel companies, custom or semi custom rifle builders, and even factory rifle manufacturers typically all have a 3 shot sub moa and in some cases sub half moa guarantee.

Now 3 shots isn't enough of a sample size to really collect data from. I know most consumers are not really dedicated shooters and believe that a 3 shot group is great for a hunting rifle.

When you extrapolate this with quantity of shots and group size, does the accepted standard then grow as the groups open up with the cone of fire?

for example
3 shot .5 moa
5 shot .8 moa
10 shot 1moa
And 30 shot plus or barrels cone 1.5 moa

Thats the data I'm interested in, not just a cherry picked 3 shot group. And I wish the manufacturers would put more effort into establishing what the true cone is.for their products, although I understand why this might not be feasible.

The Hornady ballisticians did some experimental work on this and found that group size follows a normal distribution pretty closely for a completely controlled environment with no shooter influence.




Here is the text version

​

Expected Group Size Extreme Spread​

​

3 Shot group: 60-70%
5 Shot group: 40-50%
10 Shot group: 30-40%
20 Shot group: 20-25%
30 Shot group: 15-20%
50 Shot groups: 10%​

Expected Group Size Increase​

3 shot vs 5 shot group: +15%
5 shot vs 10 shot group: +30%
10 shot vs 20 shot group: +20%
20 shot vs 30 shot group: +10%
30 shot to 50 shot group: +7%​

Link to video: I'm sure it's been discussed here somewhere before

As Form mentioned above. Starting with the average of many 3 shot groups (as opposed to a single cherry picked group) would be the only "real" way of extrapolating precision with any level of confidence.

 

[eric1115]

As Form mentioned above. Starting with the average of many 3 shot groups (as opposed to a single cherry picked group) would be the only "real" way of extrapolating precision with any level of confidence.

There is a crucial part of this, that they must be overlaid with a single POA.

Four different .50 3 shot groups do not make a .50 12 shot group unless group centers are all in the same location relative to POA.

 

[Carl Ross]

The Hornady ballisticians did some experimental work on this and found that group size follows a normal distribution pretty closely for a completely controlled environment with no shooter influence.


View attachment 685005

Here is the text version

​

Expected Group Size Extreme Spread​

​

3 Shot group: 60-70%​

5 Shot group: 40-50%​

10 Shot group: 30-40%​

20 Shot group: 20-25%​

30 Shot group: 15-20%​

50 Shot groups: 10%​

Expected Group Size Increase​

3 shot vs 5 shot group: +15% ​

5 shot vs 10 shot group: +30%​

10 shot vs 20 shot group: +20%​

20 shot vs 30 shot group: +10%​

30 shot to 50 shot group: +7%​

Link to video: I'm sure it's been discussed here somewhere before

As Form mentioned above. Starting with the average of many 3 shot groups (as opposed to a single cherry picked group) would be the only "real" way of extrapolating precision with any level of confidence.

Yes, that is the AVERAGE of those groups vs the true population. However, the error bars on what an individual group will give you get ever larger as the round count gets smaller. There's no free lunch, the higher the level of certainty you want, the larger your sample population needs to be. I like a lot of what Hornady has been publishing recently, but I think that specific part is misleading for many shooters.

 

[aschuler]

Yes, that is the AVERAGE of those groups vs the true population. However, the error bars on what an individual group will give you get ever larger as the round count gets smaller. There's no free lunch, the higher the level of certainty you want, the larger your sample population needs to be. I like a lot of what Hornady has been publishing recently, but I think that specific part is misleading for many shooters.

100% agree. That why I've gotten to the point where I choose to ignore any claims of precision that are supported by 3 shot groups...but that's more of a personal decision

The OP just asked if an extrapolation can be made. The answer (I think) is that "it can", but it's far from perfect.

 

[JF_Idaho]

This horse has been beaten to death, obviously.

I think more manufacturers have latched onto the "sub moa for a 3 shot group" disclaimer for this very reason.

Let's dive a little deeper though. Some things that cross my mind when it comes to larger shot groups, let's just use 30, is the scientific variables that are uncontrollable.

What about barrel life/throat erosion? For a barn-burner cartridge like 22-250, 30 rounds could be around 3% of that barrel life. For the more moderate calibers, lets say 1%. What does that contribute to the dispersion? What about other metallurgical properties changing? Obviously a high quality match-grade barrel is going to lessen these effects vs a factory barrel. But, we are generally talking about factory barrels in this context.

What about copper fouling? We all know new or freshly cleaned barrels can speed up after a certain number of fouling rounds. Obviously this doesn't happen at one. If a barrel gets 20, 50, 100fps faster over 100-200 rounds, it is getting a little faster after each shot. What role would this play in larger group dispersion?

Anyways, I would like to hear other's thoughts.

 

[PNWGATOR]

Wouldn’t it be simple for manufactures?!

Barrels. Scopes. Whatever…


NONE of them deliver objectively.

 

[wapitibob]

When a mfg posts a guarantee at a meaningful distance I'll take note.

 

[Formidilosus]

This horse has been beaten to death, obviously.

I think more manufacturers have latched onto the "sub moa for a 3 shot group" disclaimer for this very reason.

Let's dive a little deeper though. Some things that cross my mind when it comes to larger shot groups, let's just use 30, is the scientific variables that are uncontrollable.

What about barrel life/throat erosion? For a barn-burner cartridge like 22-250, 30 rounds could be around 3% of that barrel life. For the more moderate calibers, lets say 1%. What does that contribute to the dispersion?

Let’s use some critical thinking.

So a barrel can’t shoot 30 rounds without some magical outside influence- but we can zero it, practice with it, hunt with it, and it’s fine? How does that even make sense on the most basic level?

As to you specific example- the zero, nor dispersion changes over 30 rounds. Or a 100. 22-250’s, 22cm’s, 6UM, it doesn’t matter.

What about other metallurgical properties changing? Obviously a high quality match-grade barrel is going to lessen these effects vs a factory barrel. But, we are generally talking about factory barrels in this context.

Good barrels are good barrels. Bad barrels are bad barrels. There are plenty of $700 guns with excellent barrels.

What about copper fouling?
We all know new or freshly cleaned barrels can speed up after a certain number of fouling rounds. Obviously this doesn't happen at one. If a barrel gets 20, 50, 100fps faster over 100-200 rounds, it is getting a little faster after each shot. What role would this play in larger group dispersion?

It doesn’t materially change the dispersion. People come up with all kinds of excuses to not shoot.

 

[HingleMcCringleberry]

This horse has been beaten to death, obviously.

I think more manufacturers have latched onto the "sub moa for a 3 shot group" disclaimer for this very reason.

Let's dive a little deeper though. Some things that cross my mind when it comes to larger shot groups, let's just use 30, is the scientific variables that are uncontrollable.

What about barrel life/throat erosion? For a barn-burner cartridge like 22-250, 30 rounds could be around 3% of that barrel life. For the more moderate calibers, lets say 1%. What does that contribute to the dispersion? What about other metallurgical properties changing? Obviously a high quality match-grade barrel is going to lessen these effects vs a factory barrel. But, we are generally talking about factory barrels in this context.

This argument is like saying "I can't shoot my bow because I'll have to replace my strings/cables".

Furthermore I would counter the barrel life obsession with the possibility that if people would just pick a bullet, shoot 30rds, they would probably shoot less and know more than if they shot a dozen 3 shot groups, that tell them nothing.

What kills me is I constantly see people brag about a 3 shot group, as tiny and cherry picked as it may be, but it's never actually zeroed. Ever. The gun shoots so great...."1/4 moa all day", yet it would appear to not even be zeroed, ever. If you do not have a good zero, you have nothing.

Keep fighting the good fight Form.

 

[JF_Idaho]

Form,

Ok, well that was a lot of words just to throw out a couple insults.

So 100fps ES doesn't increase dispersion? I'm guessing dispersion is caused by magic?

Right on. Got it.

 

[JF_Idaho]

This argument is like saying "I can't shoot my bow because I'll have to replace my strings/cables".

Furthermore I would counter the barrel life obsession with the possibility that if people would just pick a bullet, shoot 30rds, they would probably shoot less and know more than if they shot a dozen 3 shot groups, that tell them nothing.

What kills me is I constantly see people brag about a 3 shot group, as tiny and cherry picked as it may be, but it's never actually zeroed. Ever. The gun shoots so great...."1/4 moa all day", yet it would appear to not even be zeroed, ever. If you do not have a good zero, you have nothing.

Keep fighting the good fight Form.

What argument?

I never said anything about not being able to shoot.....

All I was talking about is why you get a greater dispersion over a greater amount of rounds.

 

[HingleMcCringleberry]

What argument?

I never said anything about not being able to shoot.....

All I was talking about is why you get a greater dispersion over a greater amount of rounds.

If 30 rounds caused a change so drastic the shooter could tell, it would be impossible to ever zero a rifle/optic. And would definitely make "load development" impossible.

I was just pointing out that barrel life is constantly used to justify not shooting. It makes no sense.

That's all.

 

[eldeuce]

The Hornady ballisticians did some experimental work on this and found that group size follows a normal distribution pretty closely for a completely controlled environment with no shooter influence.


View attachment 685005

Here is the text version

​

Expected Group Size Extreme Spread​

​

3 Shot group: 60-70%​

5 Shot group: 40-50%​

10 Shot group: 30-40%​

20 Shot group: 20-25%​

30 Shot group: 15-20%​

50 Shot groups: 10%​

Expected Group Size Increase​

3 shot vs 5 shot group: +15% ​

5 shot vs 10 shot group: +30%​

10 shot vs 20 shot group: +20%​

20 shot vs 30 shot group: +10%​

30 shot to 50 shot group: +7%​

Link to video: I'm sure it's been discussed here somewhere before

As Form mentioned above. Starting with the average of many 3 shot groups (as opposed to a single cherry picked group) would be the only "real" way of extrapolating precision with any level of confidence.

yes, exactly! Hornady podcasts #50 and #52 are eye opening...

 

[JF_Idaho]

If 30 rounds caused a change so drastic the shooter could tell, it would be impossible to ever zero a rifle/optic. And would definitely make "load development" impossible.

I was just pointing out that barrel life is constantly used to justify not shooting. It makes no sense.

That's all.

But the whole point of this convo is that you can only zero your optic to within an inch and a half or whatever arbitrary number.

What is the cause of said dispersion?