First off, I want to again thank all of you for your help and willingness to share all of this information. It's a great help for a new guy like me.

Second, how are you measuring groups? Is there a standard way. So far I've been measuring an overall outside diameter.

Lastly, what exactly does MOA mean?

Thanks again for your help.

There are more ways to measure groups than there are ways to describe pretty girl. and most are no more quantitative either.

There is one true way for most hunters: measure the two furthest spread holes from center to center. of course it is just as accurate and easier to measure from the inside of one hole to the outside of the other hole. this is the "group diameter" even though it is not really as large as a true statistical group. then qualify it as a three or five hole group.

Regards the MOA: Minute of Angle. Fortunately for most shooters, one MOA is very close to one inch at 100 yards, and 2 inches at 200 yards. very close. Note that this would make for a 6 inch circle of bullet holes at 600 yards if your gun shoots one MOA. Note further that this is really half a MOA on either side of the center, for total MOA diameter.

Note further that there is a HUGE difference between a rifle that shoots one MOA for selected three shot groups, and a rifle that shoots one MOA for every five shot group..

I missed with my first shot,and the next four went into exactly the same place!!

[ 09-17-2003, 09:45: Message edited by: Jameister ]

On measuring groups.

I use a caliper and measure outside to outside and then subtract the caliber diameter.

Where a "problem" can arise is thinking the outside of the hole is where to measure from and to. You should measure from and to the burnish marks on the paper.

You can plainly see the dark rings on the paper surrounding the holes on the target below.

(one or these days, I'm gonna hit that dime!)

Where do you get those big dimes? I keep seeing these on reloader pages...

nice shooting!!

Birth Controller - have you ever found that the "burnish" marks aren't the same size as the caliper? Making the process of subtracting the caliber diameter from the measured outside-to-outside measurement incorrect?

GROUP SIZE ANALYSIS METHODS

(Maximum Spread)
The Maximum Spread (also called group diameter or extreme spread) is simply the distance between the centers of the two most widely dispersed shots in a group. This is the most common method used to describe group size because it is the easiest measurement to take. Unfortunately it only considers two shots in the result so an otherwise tight group of 10 shots with one "flyer" can produce results similar to a widely dispersed two shot group. For bench rest shooters who are capable of putting five shots in one hole it is a valid measure; but for the rest of us, or for handgun shooting it does not provide a "statistically significant" number for comparing targets.

(String Measurement)
This is an old method still used to determine a shooter's skill at hitting a target. It assumes the point of aim is always the desired point of impact and is simply the sum of the distances from the point of aim to each bullet hole. Originally a string was used to gather the distances, hence the name. It is still a valid measure of total error relative to the aim point. String Measurements however cannot be used to analyze sight settings because it only measures the magnitude of error, not the direction of error. It is also not a useful measure of group size because a tight group located away from the Bullseye will produce a large String Measurement.

(Average Group Radius)
The average of the distances from the statistical group center (not the aim point) to each shot is the Average Group Radius. It accurately reflects how far a typical shot will impact from the aim point with a well sighted arm. This measure is the best indicator of group size or firearm performance because flyers have less impact on the result so it provides a "statistically significant" number for comparing a series of targets or groups. Unfortunately it is difficult to calculate manually. Unlike a String Measurement, the Average Group Radius does not assume the point of aim is the desired impact point, so sighting error is not a factor in the result. Average Group Radius can therefore be used to compare group sizes when the impact point is intentionally high (rifle sighted for maximum point blank range and shooting dead center). It is also the best measure for evaluating the overall accuracy of loads. Magazine articles using Average Group Radius indicate the writer has taken care to provide readers with statistically significant data, but you should be careful not to compare it to the more common Maximum Spread.

ERROR ANALYSIS METHODS

(Vertical and Horizontal Spread)

The Horizontal and Vertical Spread of a group is simply the greatest distance between shots on the vertical or horizontal plane. This contrasts with the Maximum Spread which can be at any angle across the group. This measurement is understood by most shooters, easy to make, and can be used to help detect load and mechanical problems or "pulling" by the shooter. If the Vertical or Horizontal Spread is significantly larger and shots are well dispersed, it is called "stringing". A cross wind will obviously disperse shots horizontally. Vertical stringing may be caused by irregular powder charges and detonation problems (inconsistent ignition due to variations in primer pocket depth or primer thickness). Improper crimping, bullet inconsistencies or other loading problems usually result in larger overall group sizes, and not "stringing" in any particular direction. A loose gun sight, or broken scope may also cause stringing.

(Average Vertical and Horizontal Error)

The Average Horizontal and Vertical Error is the average of errors on the Vertical and Horizontal plane from the group's statistical center. This is a much better measure for detecting errors than Vert./Hor. Spread because the shot data is averaged to reduce the influence of "flyers". If the goal is to track "pulling" by the shooter over time or to isolate problems, then the Average Vertical & Horizontal Error is a better measurement for comparing a series of targets.

(Maximum Shot Radius)

The Maximum Shot Radius (or maximum group radius) is the distance from a group's statistical center to the center of the most distant hole. It really only indicates how far from the group center the worst shot should fall and is not a good indicator of overall performance. On a target where shots are evenly dispersed, this measurement will be about 1/2 the Maximum Spread and larger than the Average Group Radius. It is best used to quantify the worst shot in a series of targets.

(Maximum Shot Radius Compared To Average Group Radius)
The Maximum Shot Radius should be only slightly larger than the Average Group Radius. A big difference between these measures is another indication of shooter error or a bad load.

(Average Elevation and Windage Error)
The Average Elevation and Windage Errors compare a group's statistical center to the point of aim. It accurately indicates where the group center is located (or average shot impacted) with a set of vertical and horizontal dimensions. The two measurements show how well the firearm is sighted to hit the Bullseye and can be used to adjust sights if the results are converted to Minutes of Angle.

Usually the "burnish marks" on the paper are slightly smaller than the actual bullet diameter. In benchrest group matches, which are scored "maximum spread" as described above by Steve, a scoring device is used so that actual bullet diameter/center is identified and measured. R.W. Hart makes plates that attach to a modified dial caliper for this purpose. I can not link directly to the device, but if you go to this website: www.rwhart.com , then "R.W. Hart Products", then "Hart Shooting Aids", and finally "Group Measuring Device", you can kind of see what it looks like (photo is not very detailed). Their part number is RWH-X-100.

Good information, Steve.

Regards, Bill

Sure, I've noticed that. The burnish marks are considerably closer to caliber size than the holes - and I'm just an informal paper puncher / ghog hunter, so it's "close enough" for me.

(If "New Reloader" would've asked how benchrest targets were scored - I wouldn't have dared answer, because I know next to nothing about that)

The Hart measuring gear mentioned below and the in-depth treatise outlined by Mr. Ricciardelli (much of which - BTW - is concerning the difference between accuracy and precision - that "New Reloader" didn't inquire about) are both outside the scope of my interest in exactness on this subject.

FWIW ... if I error in my group measuring, it's always on the "big side".

quote:

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Originally posted by T/C nimrod:
Birth Controller - have you ever found that the "burnish" marks aren't the same size as the caliper? Making the process of subtracting the caliber diameter from the measured outside-to-outside measurement incorrect?

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[ 09-18-2003, 11:39: Message edited by: The Birth Controller ]

Here's a good article for you on group size measuring.

Group Measuring

quote:

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Originally posted by NewReloader:
First off, I want to again thank all of you for your help and willingness to share all of this information. It's a great help for a new guy like me.

Second, how are you measuring groups? Is there a standard way. So far I've been measuring an overall outside diameter.

Lastly, what exactly does MOA mean?

Thanks again for your help.

---

It's a simple matter of centering the caliper set at .224"

No different in principle than the Hart or Jones method.

quote:

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Originally posted by T/C nimrod:

quote:

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FWIW ... if I error in my group measuring, it's always on the "big side".

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Not the way you're measuring.

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BC,

You lost me on that last post....

If the caliper is "set" at .224", how do you read the distance between the center of the holes?

Thanks, Bill

Sorry for the confusion, Bill.

I'm measuring .22 caliber (.224")

If you "set" the caliper on .224" you can then position, equidistantly, the legs of the caliper over a bullet hole to determine how far outside the burnish marks you should be to establish an outer point to measure from. (It's usually very little ... a couple thousandths - the paper you use makes a difference, BTW))

This is what the Hart and Jones et al group measurers are doing with the etched circle that you center over the bullet hole. (You can see the circles etched on the glasses in the photo below of the Hart.)

It's a way of achieving near the same accurate measurement without buying a $52.00 dedicated device.

Possibly inadequate to score a formal Benchrest match, but for my informal purposes, it is plenty good enough.

TBC

quote:

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Originally posted by Bill M:
BC,

You lost me on that last post....

If the caliper is "set" at .224", how do you read the distance between the center of the holes?

Thanks, Bill

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[ 09-19-2003, 10:43: Message edited by: The Birth Controller ]

BC,

I gotcha now. You're just getting a reference on the difference between the burnished circle edges and the actual bullet diameter - so you know how much to add when you measure the outside of the "burnished" group. Definitley should give you a more accurate measurement of true group size.

Thanks for the clarification,

Bill