I've been handloading and shooting centerfire rifles from the bench for over 35 years, and although I'm not a competitive bench shooter, I know a little somthing about what you can expect from a good rifle/load combination.

Now I see a lot of people writing about 1/4" groups, many of them shooting .30 caliber and larger rifles. Groups are, of course, measured center-to-center of the two widest shots. Not that it can't be done, but quarter-inch groups are damn rare in a sporter and a lot of people seem not to realize that a .25" group with a .30 caliber rifle is, by defination, a single hole measuring only .45" across at the WIDEST. That's almost a twenty two hole smaller than a DIME. That's little, folks! Considering that the reticle on many scopes used on sporters more than subtend that measurment, it makes question how folks are measuring their groups.

I'm wondering if some of the newer generation shooters measure groups by the smallest distance between the inner edges of the bullet holes. This would make a "quarter inch" group actually measure about .46 center-to-center, an excellent group, but not a "quarter inch". A one inch group (with a .308 bullet) at a hundred yards will measure approximately .61" between the insides of the two widest shots.

How about it? Are people mistakenly, but perhaps in good faith, mismeasuring their groups?

Have to agree with you on this,on one of the other boards I see lots of "group" pictures posted,while most are darn good,one common thing they all seem to do is not measure all the way out to the true edge of hole, past "paper spring back",then subtract the bullet diameter,not the actual diameter it made in the target,which is smaller than say a .243,etc.I have come to treat this like the people that show me a 130 class deer and say it scored 150 plus.Guess in the grand scheme of things,doesn't amount to much,but this is why the BR shooters get all bent out of shape over people that have sporters that shoot less than .25 all day long(if they do their part)!!

It is interesting that something as seemingly simple as measuring center-to-center groups can be so hard for some people to perform. I don't get too bent out of shape when someone brags about their "1/4 inch group all-day-long rifle", I just invite them to a match, and offer to pay their match fee. They never take me up on it?...

Heck, it happened yesterday, went something like this. I showed a couple decent groups (both sub 1/2 moa) that I shot Monday with 308 M77VT to a friend, and he said that was nothing - his PSS 308 shoots way better than that!
Well, bring it on, shoot a Hunter class match w/us!...
Nope, My eyes aren't so good, I can't do it with my 6.5-25X scope on 6.5X.
How do you know, you've never seen the target?
Nope, can't see it with 6.5X.

I tend to discount their stories after that!

Good posts!,

Bill

I have also seen this happen too many times at our range . And the one that is most common is that they show you groupes fired at the 50 m backstop , Sure is easy enough to keep them in less than halve an inch all day long with a sporter , and good handloads . But then again take that 1/2" group at fifty that the shooter brags about , calculate it over a 100 m , and you might get a 1MOA , if the shooter does his part . Good luck, and I always say , either put up or shut up

Rudie

Howdy,

Great post stonecreek!!!
Several years ago, I read a book, the title of which escapes me, that advocated measuring outside edges then subtracting one caliber...but, the author insisted that he should do it in the verticle plane only. Not furthest outside spread, but in verticle only!! His argument was that this eliminated all wind effect! I'm a little skepticle, but would like to hear what you folks think of the idea, and the reasoning behind it.

Coach

There are several different ways to measure a group size:

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.

I think sometimes a guy will "stretch" (or shrink in this case) the truth a little bit.

But I think the *main* source of the mythical 1/4 MOA rifle is the guy that fired ONE 3-shot group ONE time that made the 1/4" mark. He now has himself a JENN-U-WINE 1/4" rifle, and is willing to tell it to anyone that will listen.

Every time after that "something musta happened", cause he KNOWS that he has a 1/4" shooter in his hands.

Thanks for the responses. I was beginning to think I was the "odd" man out on this subject, judging from all those "1/4 inch" group reports. I'm not ashamed to say that, in over 35 years and having owned some very precision rifles, I've NEVER fired a .25" group. My best, with a .222, was perhaps just under .3 inch. But I'll guarantee you, when I got my .375 H & H to stay consistently within and inch, I knew I had one shooting in the top 10% of all the .375's out there. My son's .30-06 sporter will do about .75" with it's best loads (that's well under a half-inch space between holes), and I'm not expecting anyone I know to come along with an '06 sporter and top that any time soon.

As I say, small groups can be done, but there seems to be an inordinate amout of BS floating on this subject.

Geez, my keyboard will shoot WAYYY bettr'n that!

I have the most problems measureing "one holers". Fortunately, they don't happen too often. For the rest, if you measure "inside to outside" of the two holes farthest apart, the paper spring back thing doesn't matter. As long as you measure on the same spot on both holes everything is copastetic.

I just wish:
1) that I could shoot as good as my rifles, and
2) my rifles could shoot as well as my keyboard....

FWIW, Dutch.

I measure my groups center to center and average several groups when I say what my gun will shoot.I too have seen several people that shoot one fluke group and claim to have a 1/4" or 1/2" rifle.Most can't duplicate the group and the average usually ends up in the 1" and over range.

aww hell.. you KNOW the first liar aint got a chance.

take the gross measurement, subtract one bullet diameter, and call it whatever.

Why this open approach? well, let's see... YOU tell me exactly, in inches, how big an MOA is?

hint, it's bigger than 1.00000000000 inches.

but, crap guys, if you say "my whizbagger shoots .5 moa" the next guy will tell you his remachester shots .45, but only on windy days, but in a tunnel is a ones guns.

I HAVE a ones gun... my wife can shoot ones with it all day... in my hands, it's a twos gun... and yeah, it's an unlimited br gun....

but, I have a threes gun in 257 and several six's guns.

jeffe

Coldbore,
You got the drop on me. And the hundredths are MORE than the difference that this string started with. original statement was .45 vs .46 overal, and saying it was under 1/4" moa on a .308 round. BOTH are, when you measure moa in reality. The group would have to be larger, gross, than .558.

But, as always, the first liar doesnt have a chance. If someone wants to call their hunting rifle 1/2moa and it shoots 3/4moa, what's the difference? 1" at 400 yards!

just my 2�
jeffe

Ricciardelli, I have a question. When you measure group size by the Average Group Radius and Maximum Shot Radius methods, how do you accurately determine the statistical group center? Do you have a method that tells you exactly where the statistical group center is, or do you sort of guesstimate it by looking at your group and saying to yourself, "Looks like my statistical group center is right about there", and you poke your finger at the spot on your target.

Say I'm shooting my .223, and I have the POI about 2" above the POA at 100 yards, and my 5 shot group has a Maximum Spread of 1 1/4". I believe I could very easily get my statistcal group center wrong due to one or two flyers (not big flyers but little flyers if there is such a thing). Also, I could get it wrong by thinking my POI is 2" above my POA, but actually the POI is 2 3/8" high. Trying to accurately find the statistical group center of groups at 300 yards would be impossible. Especially if you were to see MY groups.

Am I missing something here or am I just thick headed. roy p.

Center to Center. I always measured from Outside to outside, since that seems to be a part of the "hole". I would also drop the one or two flyers from the group as a whole too.

Difranco

I guess dropping one or two shots from a group is the equivalent of a "Mulligan" in golf?

Now that I understand how to drop unwanted shot from my groups, ALL of my rifles will do a quarter inch!

When I'm not using the time-honored "shoot five and measure your best two" method, I simply measure to the outside carbon rings and subtract bullet dia.

I figure the carbon is where the bullet made actual contact with the paper.

Difranco:

In many statistical analyses, dropping the extremes then averaging the remaining data is a valid and useful methodology.

Not so with rifle shooting, especially with the typical five shot group: The value of determining group size is to determine the likelihood (consistency) of hitting a given target of given size at a given range. If three of five shots will do this, say 100% of the time, but two of five shots will miss 100% of the time, then your chance of hitting the mark is 60%.

On the other hand, if 5 of 5 strike the target, although with a greater extreme spread than the 3 of 5 in the other example, then your chance of hitting the mark is 100%.

The time-honored method of describing the accuracy of a rifle is to measure the extreme spread of a group of a given number of shots.

Expressing rifle grouping ability in any other way, even if valid statistically, is an apples-to-oranges comparison and is misleading to someone who assumes the standard method.

(I don't play golf either, but I think a Mulligan is a sort of "oops, that one didn't count did it fellas, so we don't have to put it down as a stroke?")

Stonecreek Im damn glad you made this thread, my groups are getting better just reading this cause Ive been measuring outside to outside. Lets see that would make this one sub-sub 1/4"