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Different way of calculating a group size

This is a discussion on Different way of calculating a group size within the Accuracy forums, part of the M14 M1A Forum category; Gentlemen, You must remember that when you use the "Extreme Spread" method, your answer is highly dependent on the sample size. As you increase the ...


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Old April 8th, 2017, 01:00 PM   #16
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Gentlemen, You must remember that when you use the "Extreme Spread" method, your answer is highly dependent on the sample size. As you increase the sample size, the extreme spread generally increases until you get to approx. 70 samples. The "Mean Radius" method does not have such a high dependence on the sample size. Rick

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Old April 8th, 2017, 04:39 PM   #17
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Originally Posted by Allen Humphrey View Post
Badger,

The method you describe is called "mean radius" or "average radius" calculation. I use it and believe it is an excellent way to evaluate accuracy, especially for iron sights. There is some free software available that makes the process much quicker. Think it's called On Target.
Thanks, I'll try out that software. I calc'd six targets by hand yesterday with a ruler and it took me an hour and a half.

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Old April 8th, 2017, 05:16 PM   #18
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Originally Posted by JayKosta View Post
---------
Yes, 'group size' is the 'extreme spread' (distance) between the 2 shots of a group that are farthest apart.

The other methods of calculating the 'shot distribution' within a GROUP of shots are similar to 'Quality Control' statistics for production of parts to meet a particular specification.
Those statistics are useful to predict how many parts will be 'in spec' and how many fall 'out of spec', for all the parts in the group.

For shooting 'groups' it would be something like saying -
80% of the shots are in a 2 moa area,
90% are in 3 moa, and
100% are in 6 moa.

And it does depend on what is trying to be determined.

Jay Kosta
Endwell NY USA
Jay, If it helps to think of "Mean Radius" as being akin to a quality control methodology, that's fine. Both quality control methodologies and "Mean Radius" calculations are based on statistics. However, "Mean Radius" is as valid a method of determining group size as "Extreme Spread". It is just doing it differently. Both yield numerical results that characterize the "tightness" of the shot group. One method (Extreme Spread) characterizes the group using only two shots and basically ignores all other shots. If you have a very tight group but have one "flier", you have the same numerical result as if all shots were dispersed throughout the space between the two extreme shots. That can be problematic since it puts a huge amount of emphasis on one shot. "Mean Radius" characterizes the group size in a statistical fashion and each shot basically has equal value in the final numerical result. The application should dictate what is the best method. Rick

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Old April 8th, 2017, 05:17 PM   #19
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Originally Posted by WaM14gunner View Post
I will stick with the tried and true center to center method of farthest apart holes.
It's not optimal because of flyers. Yesterday I shot two 10-round targets at 100 yards. I shot one group of hand loads. 8 shots made a 2 MOA extreme spread group. I had two flyers, one at about 3 o'clock and one at 9 o'clock. each flyer was about two inches away from the central 8 shot group. Extreme spread is 6 MOA but I consider that shooting to be 2 MOA.

Next 10 shots was Federal GMM. NO flyers and about 2.5MOA group size of even distribution.

What the above tells me is that my hand loads are generally better but I still have some QC to work on. The mean average method is useful.

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Old April 8th, 2017, 07:58 PM   #20
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Dude. Stop.
Shoot a five shot group.
Use the same point of aim, proper sight alignment, sight picture, and trigger control. call your shots. If you sent a flyer don't count it in your group. When you can shoot a 1" to 2" group at 25 yards (4 to 8 moa) you don't have to stay home an be a cook and your ready to move on. Until you can get to that point no amount of fancy math is going to do you a bit of good. For that matter if you can't do the math while your behind your rifles sights it's probably not useful in the field and should on some report on McNamara's desk.

PS. Have a blast at your Appleseed course next week hopefully it's not pouring down rain like it was here in California today.

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Old April 8th, 2017, 08:02 PM   #21
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Originally Posted by Badger5th View Post
It's not optimal because of flyers. Yesterday I shot two 10-round targets at 100 yards. I shot one group of hand loads. 8 shots made a 2 MOA extreme spread group. I had two flyers, one at about 3 o'clock and one at 9 o'clock. each flyer was about two inches away from the central 8 shot group. Extreme spread is 6 MOA but I consider that shooting to be 2 MOA.

Next 10 shots was Federal GMM. NO flyers and about 2.5MOA group size of even distribution.

What the above tells me is that my hand loads are generally better but I still have some QC to work on. The mean average method is useful.
Where did the flyers come from? Was it ammo, gun or something you did? Are you shooting from a vise? And how many inches is your group across if you use a ruler not a calculator? Is it 2", 4" or 8".

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Old April 9th, 2017, 07:49 AM   #22
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Originally Posted by rickgman View Post
...
However, "Mean Radius" is as valid a method of determining group size as "Extreme Spread". It is just doing it differently. Both yield numerical results that characterize the "tightness" of the shot group.
...
--------------
Hello Rick,

Yes 'mean radius' is a good way to 'characterize' a shot group.

But the term 'group size' shouldn't include analyzing the distribution of the shots in the group - it's just the measured size of the group. I think the statistics about analyzing the group are very useful, but they don't change the group size.

If someone claims to be able to shoot x moa groups, then I expect ALL the shots to hit within an x moa circle (ES).

About 'called flyers' - yes they can be excluded from the group IF you do so BEFORE spotting the hit. E.g. you know you pulled the shot, or there was an obvious mechanical problem involving the shot.
If a shot lands outside of the area you want and you thought it was a 'good shot', then it's probably just one of the expected statistical 'outliers' that make ES size approx 3X 'mean radius' size.

Jay Kosta
Endwell NY USA

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Old April 9th, 2017, 07:50 AM   #23
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Originally Posted by xXRiflemanXx View Post
For that matter if you can't do the math while your behind your rifles sights it's probably not useful in the field and should on some report on McNamara's desk.
McNamara's desk brings back a lot of memories.

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Old April 9th, 2017, 09:48 AM   #24
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Originally Posted by Badger5th View Post
It's not optimal because of flyers. Yesterday I shot two 10-round targets at 100 yards. I shot one group of hand loads. 8 shots made a 2 MOA extreme spread group. I had two flyers, one at about 3 o'clock and one at 9 o'clock. each flyer was about two inches away from the central 8 shot group. Extreme spread is 6 MOA but I consider that shooting to be 2 MOA.

Next 10 shots was Federal GMM. NO flyers and about 2.5MOA group size of even distribution.

What the above tells me is that my hand loads are generally better but I still have some QC to work on. The mean average method is useful.
I agree completely with Jay's most recent post, and that one measurement method is perfect for all situations.

If you've got two true "flyers" within the same shot string, then there's something very wrong with the shooting position, shooting conditions, technique, etc. If an external event doesn't cause the rifle to fire (or cause you to pull the trigger when you really don't want to) or the rifle to move unintentionally exactly as the shot is taken, it's not a flyer, and should be included with all other bullet impacts within the shot string.

If while evaluating a handload, I put four shots into 1/2" and a fifth one impacts an inch away from the other four (with it feeling like a good shot), it's a 1 1/2" group. This particular group may show enough promise to warrant an additional group to be fired with it, but I in no way call it a 1/2" group. If one shot within a group of five doesn't feel right and I don't confirm where that bullet impacted, I'm not going to look at the target after the string is finished and assume that an impact away from the others is the one that didn't feel right.

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Last edited by Grizzman; April 9th, 2017 at 10:25 AM.
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Old April 9th, 2017, 11:10 AM   #25
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Originally Posted by JayKosta View Post
--------------
Hello Rick,

Yes 'mean radius' is a good way to 'characterize' a shot group.

But the term 'group size' shouldn't include analyzing the distribution of the shots in the group - it's just the measured size of the group. I think the statistics about analyzing the group are very useful, but they don't change the group size.

If someone claims to be able to shoot x moa groups, then I expect ALL the shots to hit within an x moa circle (ES).

About 'called flyers' - yes they can be excluded from the group IF you do so BEFORE spotting the hit. E.g. you know you pulled the shot, or there was an obvious mechanical problem involving the shot.
If a shot lands outside of the area you want and you thought it was a 'good shot', then it's probably just one of the expected statistical 'outliers' that make ES size approx 3X 'mean radius' size.

Jay Kosta
Endwell NY USA
Well said.

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Old April 9th, 2017, 12:35 PM   #26
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Originally Posted by xXRiflemanXx View Post
Where did the flyers come from? Was it ammo, gun or something you did? Are you shooting from a vise? And how many inches is your group across if you use a ruler not a calculator? Is it 2", 4" or 8".
My sight alignment, sight picture and trigger squeeze were good. I was shooting from a bench with a front bag. I suspect it was QC issues with my hand holds. I (almost) never have flyers with commercial ammo. The extreme spread in the case I mentioned was 6". Without the two flyers it was 2".

At 25 yards I get one hole groups.

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Badger

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Old April 9th, 2017, 12:47 PM   #27
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Originally Posted by xXRiflemanXx View Post
Dude. Stop.
Shoot a five shot group.
Use the same point of aim, proper sight alignment, sight picture, and trigger control. call your shots. If you sent a flyer don't count it in your group. When you can shoot a 1" to 2" group at 25 yards (4 to 8 moa) you don't have to stay home an be a cook and your ready to move on. Until you can get to that point no amount of fancy math is going to do you a bit of good. For that matter if you can't do the math while your behind your rifles sights it's probably not useful in the field and should on some report on McNamara's desk.

PS. Have a blast at your Appleseed course next week hopefully it's not pouring down rain like it was here in California today.
Most of my shooting with my M1A with 10 shot groups is under 3 MOA at all ranges up to 100 yards. Closer to 2 MOA with the mean radius method as discussed in this thread. Regarding the Appleseed thanks for your good wishes. Got my 10/22 balls on zeroed at 25M on 1-inch squares this weekend.

Regards,
Badger

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Old April 9th, 2017, 12:54 PM   #28
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Quote:
Originally Posted by Badger5th View Post
My sight alignment, sight picture and trigger squeeze were good. I was shooting from a bench with a front bag. I suspect it was QC issues with my hand holds. I (almost) never have flyers with commercial ammo. The extreme spread in the case I mentioned was 6". Without the two flyers it was 2".
...
------------------
I understand that to mean that YOU can shoot 2 inch groups with good ammo, but the 'group size' with your hand loads was larger.

I think it's important for us to have a 'common understanding' of our terminology. It allows us to talk about things so we all have the same understanding of the words and ideas.

Jay Kosta
Endwell NY USA

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Old April 9th, 2017, 03:04 PM   #29
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Originally Posted by xXRiflemanXx View Post
Dude. Stop.
Shoot a five shot group.
Use the same point of aim, proper sight alignment, sight picture, and trigger control. call your shots.
Rifleman hits it on the head. I will add to this. My coaches have drilled this into my head and honestly the more I learn, the more profound it becomes. There are only TWO Principles of Marksmanship, which of course, all the fundamentals reside. TWO Principles:

Sight Alignment

Trigger Control


SIGHT ALIGNMENT: Align the sights properly every time and point it in the same place every time and you'll hit the target. (environmental factors notwithstanding)

TRIGGER CONTROL: Move the trigger without disturbing the sights and youll hit your target.

If you miss, its because you're screwing up one or both of these principles.


****************
To give my statement a bit of depth-

Sight Alignment includes: Steady position, proper sight picture, dont breath while youre breaking your shot, hard firm cheek wield, etc

Trigger control includes: Proper grip, proper finger placement on trigger, moving the trigger straight and smooth.

People love to talk fancy, but from what Ive seen (and i LOVE target gazing at ranges) 90 percent of folks need to become proficient at these two principles before they can talk about anything else. Most of the time, its you, not the gun and ammo.


My 2 cents.

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Old April 9th, 2017, 05:15 PM   #30
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Originally Posted by Whatsinaname181 View Post
There are only TWO Principles of Marksmanship, which of course, all the fundamentals reside. TWO Principles:

Sight Alignment

Trigger Control
Do not forget Sight Picture which is the third main principle of marksmanship. If the sights are aligned but not pointed at precisely the right spot, things are only half done.

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