Different way of calculating a group sizeThis is a discussion on Different way of calculating a group size within the Accuracy forums, part of the M14 M1A Forum category; I don't know if someone has come up with this method before but I believe it works mathematically.
1. Fire 10 shots.
2. On the ... 

April 7th, 2017, 08:23 PM

#1  Platoon Sergeant
Join Date: Jan 2017 Location: Eastern Mass
Posts: 338
 Different way of calculating a group size
I don't know if someone has come up with this method before but I believe it works mathematically.
1. Fire 10 shots.
2. On the target draw an X & Y axis through one bullet hole.
3. From that X/Y axis measure the X and Y distance to each of the other 9 bullet holes. Write them down in a table format. Make sure you use correct positive and negative values as appropriate.
4. When done add up all the X values and all the Y values into two totals. Remember the X & Y value for the shot hole you selected in step two above will be 0,0.
5. Divide each total by 10.
The answer will be the X/Y coordinates of the mathematical center of the shot group RELATIVE TO the bullet hole you selected in step 2.
Moving on.
6. Mark the center of the group on the target.
7. Measure the distance from the group center mark to the center of each bullet hole. Record the data as you go.
8. When you are done add all the numbers up and divide by 10. This will be the mathematical average radius of the shot group.
9. Multiply by 2 to get the mathematical average diameter of the shot group.
10. Divide the answer in step 9 by 1.045 to get the group size in MOA.
What do you guys think? Does this seem like a legitimate method? When I calculated some of my targets that way I went from 33.5MOA based on extreme spread to 22.2 MOA. It seems to me to be a fair method of handling fllyers. Makes me feel better about my shooting in any case.
Regards,
Badger

 
April 7th, 2017, 08:52 PM

#3  Old Salt
Join Date: Dec 2008 Location: Southeast
Posts: 1,949

Let's suppose you have 4 concentric shots on the 2" circle and 4 shots on the 4" circle. Your average r is 3" or group average d is 6". However your real group size is r is 4" and d is 8". Using the average as in your method works in your favor.
Finding the centroid of the shot group as you describe in part 1. is a handy step to take when adjusting sights. Instead of cranking the sight at the range it's always better to take your target home do that exercise and then move the sight.
Thanks for posting.

 
April 8th, 2017, 06:18 AM

#4  Lifer
Join Date: Mar 2009 Location: Endwell NY
Posts: 2,191

That method calculates 'something' but NOT 'group size'.
Group Size is the diameter of the smallest circle that will cover ALL of the shots.
Jay Kosta
Endwell NY USA

 
April 8th, 2017, 06:50 AM

#5  Automatic Rifleman
Join Date: Oct 2016 Location: Dry side of Washington
Posts: 130

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.

 
April 8th, 2017, 07:04 AM

#6  Old Salt
Join Date: Sep 2014 Location: Michigan
Posts: 1,126
 Quote:
Originally Posted by JayKosta That method calculates 'something' but NOT 'group size'.
Group Size is the diameter of the smallest circle that will cover ALL of the shots.
Jay Kosta
Endwell NY USA  Jay, What you call "Group Size" is technically "Extreme Spread". There is also another recognized method of determining group size and that is called "Mean Radius". Each has its advantages and disadvantages. It all depends on what you are trying to determine. Rick

 
April 8th, 2017, 07:15 AM

#7  Designated Marksman
Join Date: Feb 2014 Location: South Texas
Posts: 622
 Quote:
Originally Posted by Badger5th I don't know if someone has come up with this method before but I believe it works mathematically.
1. Fire 10 shots.
2. On the target draw an X & Y axis through one bullet hole.
3. From that X/Y axis measure the X and Y distance to each of the other 9 bullet holes. Write them down in a table format. Make sure you use correct positive and negative values as appropriate.
4. When done add up all the X values and all the Y values into two totals. Remember the X & Y value for the shot hole you selected in step two above will be 0,0.
5. Divide each total by 10.
The answer will be the X/Y coordinates of the mathematical center of the shot group RELATIVE TO the bullet hole you selected in step 2.
Moving on.
6. Mark the center of the group on the target.
7. Measure the distance from the group center mark to the center of each bullet hole. Record the data as you go.
8. When you are done add all the numbers up and divide by 10. This will be the mathematical average radius of the shot group.
9. Multiply by 2 to get the mathematical average diameter of the shot group.
10. Divide the answer in step 9 by 1.045 to get the group size in MOA.
What do you guys think? Does this seem like a legitimate method? When I calculated some of my targets that way I went from 33.5MOA based on extreme spread to 22.2 MOA. It seems to me to be a fair method of handling fllyers. Makes me feel better about my shooting in any case.
Regards,
Badger  Sounds like a cool way to get a mean average which will give you a lower number than the "usual" measurement for extreme center to center (which includes your fliers).
Now throw into your calculation 3 sigma standard deviation for your most possible extreme group size and then you will be happier with the usual extreme group measurement.
Thanks

 
April 8th, 2017, 07:23 AM

#8  Master Gunner
Join Date: Apr 2012 Location: El Paso TX
Posts: 884
 Quote:
Originally Posted by Allen Humphrey 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.  On Target is too easy to use. Scan the target, click a couple buttons, boom group size calculated.
Plus with On Target, I can keep my boots on since it does the math for me.

 
April 8th, 2017, 07:31 AM

#9  Old Salt
Join Date: Apr 2015 Location: North Carolina
Posts: 1,760
 Quote:
Originally Posted by Badger5th I don't know if someone has come up with this method before but I believe it works mathematically.
1. Fire 10 shots.
2. On the target draw an X & Y axis through one bullet hole.
3. From that X/Y axis measure the X and Y distance to each of the other 9 bullet holes. Write them down in a table format. Make sure you use correct positive and negative values as appropriate.
4. When done add up all the X values and all the Y values into two totals. Remember the X & Y value for the shot hole you selected in step two above will be 0,0.
5. Divide each total by 10.
The answer will be the X/Y coordinates of the mathematical center of the shot group RELATIVE TO the bullet hole you selected in step 2.
Moving on.
6. Mark the center of the group on the target.
7. Measure the distance from the group center mark to the center of each bullet hole. Record the data as you go.
8. When you are done add all the numbers up and divide by 10. This will be the mathematical average radius of the shot group.
9. Multiply by 2 to get the mathematical average diameter of the shot group.
10. Divide the answer in step 9 by 1.045 to get the group size in MOA.
What do you guys think? Does this seem like a legitimate method? When I calculated some of my targets that way I went from 33.5MOA based on extreme spread to 22.2 MOA. It seems to me to be a fair method of handling fllyers. Makes me feel better about my shooting in any case.
Regards,
Badger  Mean radius https://www.scribd.com/document/1571...ccuracyMetodo 
 
April 8th, 2017, 08:26 AM

#10  Lifer
Join Date: Sep 2009 Location: Arkansas
Posts: 3,612
 Quote:
Originally Posted by ArmyPilot Plus with On Target, I can keep my boots on since it does the math for me. 
Dude, if ya gotta get to 15 or 20 you need to get to the range more often!

 
April 8th, 2017, 08:29 AM

#11  Old Salt
Join Date: Nov 2016 Location: Washington
Posts: 1,360

I will stick with the tried and true center to center method of farthest apart holes.

 
April 8th, 2017, 08:51 AM

#12  Platoon Commander
Join Date: Aug 2014 Location: Lynnwood Washington
Posts: 415

Too much math! Just use a quarter or a dime, maybe even a nickel. Anything over that and you are shooting like me.

 
April 8th, 2017, 09:02 AM

#13  Lifer
Join Date: Mar 2009 Location: Endwell NY
Posts: 2,191
 Quote:
Originally Posted by rickgman Jay, What you call "Group Size" is technically "Extreme Spread". There is also another recognized method of determining group size and that is called "Mean Radius". Each has its advantages and disadvantages. It all depends on what you are trying to determine. Rick  
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

 
April 8th, 2017, 09:03 AM

#14  Lifer
Join Date: Jul 2013 Location: Illinois
Posts: 3,329

I started measuring after each shot and I've found it's done wonders for my consistency. I'm a .30 moa all day long now.

 
April 8th, 2017, 12:08 PM

#15  Lifer
Join Date: Aug 2016 Location: south east Florida
Posts: 2,822

hell badger,anything after 10 i gotta take my shoes off here

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