Measuring Group Size

[brstevns]

What is the best way to measure group size ?

[shoot-n-lead]

In club matches...measured to the outside edge of the widest point in the group and them subtracted the bore diameter.

Not sure this is the best...but it is what was used.

[Calamity Jake]

^^^^^This is the best way but you subtract the bullet diameter not bore diameter.

[Texas by God]

That's how we do it-widest spread minus bullet diameter. When you get 3 under bullet diameter you smile big......

[Artful]

Are you measuring for Pistols?
http://www.bullseyegear.com/bullseye...2&cat=7&page=1

Airgun
http://www.champchoice.com/store/Mai...ns&item=133ROM

http://www.championshooters.com/inde...110&Itemid=111

the above scoring system is what most of us use for group size.

[brstevns]

Measuring for rifle. So measure from outside edge of the 2 the most distant holes and subtract bullet diameter, am I correct ?

[Calamity Jake]

Artful, your a good man and I hate to say it but none of the above will measure group size!!!

[Calamity Jake]

Measuring for rifle. So measure from outside edge of the 2 the most distant holes and subtract bullet diameter, am I correct ?

You are correct!!!

[wv109323]

Those templates are to determine if a bullet touches a scoring ring to determine value. Group size is measured for size for a number of shots regardless of their distance from point of aim.

[country gent]

I measure from inside edge of one hole to outside edge of the farthest hole its a direct reading then. There are adaptors for a set of calipers that are clear with scored bullet dias for measuring group size. line each scored hole up over the 2 widest holes and read the calipers.

[M-Tecs]

Various methods are used and greatly argued over. Level of precision mostly determines best method. On larger groups the inside edge to the outside edge of the two widest shots is the simplest. Outside to outside subtracting the bullet diameter works great on wadcutter's but on some targets even the burnished edge of the paper is smaller than the bullet diameter if you measure a single hole.

http://yarchive.net/gun/rifle/benchr...rget_meas.html

http://www.6mmbr.com/ontargetsoftware.html

http://www.neiljones.com/html/target_measuring.html

http://www.thetruthaboutguns.com/201...ng-group-size/

http://forums.accuratereloading.com/...043/m/73010476 post 18 has various methods

[lotech]

The entire process may be a bit flawed. That may matter to some, but not to others. I give in and measure the way most describe, but use a ruler graduated in both tenths and twentieths of an inch. This was mentioned in a book, "Cast Bullets for Beginner & Expert" by Joseph Brennan. Using a caliper to measure groups is not a method that will give exactly repeatable readings. Also, try measuring actual bullet hole diameters in the paper, regardless of whether it is target paper or something else such as copy paper. The holes are somewhat smaller in diameter than actual bullet diameter.

[44MAG#1]

Unless one is in a scanctioned match who cares how the groups are measured? I measure outside to outside of the widest holes and call that group size.
I don't shoot in competition so I measure the way I want to. So what if the measurements are a few thousands off. I am measuring for my own use and my way is accurate enough for this old silly person.

[N21911S]

I use On Target Precision Calculator from here: https://ontargetshooting.com/. $12 is really cheap for what it does. I bring my targets home and scan them. Open the file with On Target, measure them and record the results. Most importantly, it calculates mean radius of the group, which is a much more accurate way of determining the quality of the group. And it also calculates extreme spread. The process of measuring a group takes less than a minute. I have no relationship with On Target except for being a satisfied customer.

[Ballistics in Scotland]

There is no such thing as a group measurement system which gives a perfect measuring system for all purposes. With all kinds though, a ten-shot group is far, far more statistically valid than a three-shot or five-shot one.

The usual measurement in the days of scheutzen shooting was string measurement. This consisted of the average measurement from the centre of the aiming point to the centres of the bullet holes. This takes into account the rifle still pointing where you think it ought to point, which for most people is a good thing.

If it is desired to eliminate this, you can similarly measure the mean distance from a point chosen as the centre of the group. There are various ways of choosing this point, but one is to eliminate the highest and lowest shot, and take the line mid-way between the second lowest and second highest as the horizontal axis. Then for the vertical axis which crosses it, do the same with furthest left and furthest right.

Both of these place a premium on consistency by reducing the importance of the occasional flier. The legitimacy of this depends on what you need. If you are hunting deer, you may think the occasional flier by six inches or so at long range, which could mean a lost cripple or the head of a lifetime untouched, is terrible, and a reliable group of two or three inches doesn't matter in the least. If it is prairie dogs at long range, the occasional one going about his business unscathed may be fine if the group is mostly tight.

For rimfire target shooting I used to use a gauge, which is a bullet diameter plug inserted with a long, flexible spring so that wishful thinking wouldn't push it sideways in the ragged hole a .22 makes. It had a lens to magnify the point where could contact the black line on the target. No doubt they can be had with a central point as well.

[brstevns]

In the past I have always measured from outside of the two most distant bullet holes. Then I was told I was doing it all wrong? That is the reason I asked the original question.

[PtMD989]

Unless one is in a scanctioned match who cares how the groups are measured? I measure outside to outside of the widest holes and call that group size.
I don't shoot in competition so I measure the way I want to. So what if the measurements are a few thousands off. I am measuring for my own use and my way is accurate enough for this old silly person.

X2


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[fatelvis]

I use my digital calipers, open them to the bullet diameter, zero it, and then measure the outside of the most distant bullet holes.
No math needed.

[M-Tecs]

This may sound funny until you think about it. To check your method measure a one shot group. The result needs to be .000"

If you method gives you something other than .000" you are introducing inaccuracies in what you are doing.

On a 38 caliber wadcutter if you measure to the outside without subtracting the bullet diameter you added .358" to your .000" group.

On the other hand if using a bullet profile that doesn't cut a clean hole and you measure to the outside and subtract .358" you would have a minus sized group since the hole normally somewhat smaller than the bullet diameter.

[Thumbcocker]

Don't use any type of measuring tool.
those suckers will cause group expansion as soon as they touch the paper. I can't count the number 1.5" inch groups I have had jump to 3.5" as soon as a measuring tool hit the paper.