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/bullseyepistol/product.php?productid=112&cat=7&page=1

Airgun
http://www.champchoice.com/store/Main.aspx?p=ItemDetailOptions&item=133ROM

http://www.championshooters.com/index.php?option=com_virtuemart&view=productdetails&virtuemart_product_id=1160&virtuemart_category_id=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/benchrest_target_meas.html

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

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

http://www.thetruthaboutguns.com/2014/04/jeremy-s/non-pro-tip-measuring-group-size/

http://forums.accuratereloading.com/eve/forums/a/tpc/f/2511043/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 [emoji106]


Sent from my iPhone using Tapatalk

[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.

[jim147]

Dime, nickel and quarter.

[Hardcast416taylor]

Ever since I actually cared about how big my grouping was I was told the following method. Using a flat ruler of some sort, measure from the center of the two farthest apart holes. Been doing it this way almost 60 odd years. I`m sure that a nice buck you just took really cared if your target group size was measured one way or another.Robert

[brstevns]

What do people consider a decent 100 yard group ?

[PtMD989]

I'm no expert but I'd be really happy with a 1 in. 3 shot group with out shooting from a bench. With my MZ.


Sent from my iPhone using Tapatalk

[robg]

What do people consider a decent 100 yard group ?
It depends on what gun I'm shooting 2 -3 inches with my 357 mag,1-1.5 inches with my 308,1inch with my 223.but I know they can all shoot better than that but I can't.

[M-Tecs]

What do people consider a decent 100 yard group ?

The depends on the firearm, bullets and use.

With an original Trapdoor Springfield I am happy with 3 inch five shoot group. Same rifle rebarreled I expect about half that. That is using cast.

With my long range target rifles using jackets anything over 1/2" for ten shoot group concerns me.

With my BPCR and cast with black 1 1/2" five shot groups makes me happy.

For my centerfire varmint rifles I want 5/8 and under. I do have a Krieger Barreled AR that started life as a 3/8 MOA rifle. It has shot a bunch of 1/4" groups but not on demand. It has around 10,000 rounds through it. The throat is in tough shape but it is still holding 7/8" to 1" MOA. With that high of round count I am still happy with the groups. As soon as I am not I will chamber and install a new one.

[Mk42gunner]

Kind of late here, but I use two different methods to measure groups. The first is the common measure the furthest two holes and subtract bullet diameter. The second is to measure the width of the group and the height of the group, I tend to think that gives more information.

As an example, you have a ten shot group that is 3½", not very good right? But what if it is 3/4" high and 3½" wide? Sounds more like a wind doping problem than a rifle problem all of a sudden, doesn't it?

Robert

[popper]

I scan my targets, use the free version of OnTarget, save to a thumb drive. I add the calculated group size to my load spreadsheet with notes. Separate sheet for each gun. Someday when I get bored I'll link the load to the target pic.

[NoAngel]

What do people consider a decent 100 yard group ?


Depends on the gun and the person's point of view. For me, under 2 inches at 100 is good. Under an inch is awesome. I also think 3 shot groups are a bit of a joke. They tell lies. Lots of guns can shoot well for 3 to 5 shots. Can that rifle do that well under the pressure of hard use?

I shoot minimum 10 shot groups. Depending on the rifle, I may shoot 20. I group my AR's with a 20 round magazine.

Everyone has their opinions and they are just that, opinions, but for ME, a rifle that will put 20 rounds[fired in less than 10 minutes] inside 2 inches at a hundred beats a rifle that shoots a little clover leaf three hole group but needs time to cool before doing it again.

[M-Tecs]

I have a 308 Savage 99 that start to walk badly by the third round. I could care less. This is a deer hunting rifle only. Never fired more than one round at a deer with this rifle. On this would I am only interest in were the first shoot goes. Second shot most likely would be a running target. Hard use for this rifle would a second shot.

[TCLouis]

Since I am only measuring to compare loads to find something to either plink or hunt, I have a simple method use a tape to measure to the farthest outside edge and look at the group shape. Is it me or are the best groups either triangular or round in shape.

Much shortened to the final point of his story, but years ago Jack O' Connor said what counted with a hunting rifle was 5 one shot groups.
Because when one is hunting the accurate placement of the first shot is what really counts.

[Triggernosis]

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.

Hell yeah, and throw out those fliers too!

[mac1911]

Hell yeah, and throw out those fliers too!
you have to at least throw out the worst couple...... heck I went from 5.5moa with my Arisaka to 4.1 moa just by tossing those flyers...
I use a old version of on target.
heres the one with 16.7% of the worst shots dropped :veryconfu
http://i.imgur.com/OJ9oNz6l.jpg

[Snow ninja]

Wait, you all have more than one hole to measure? My group size is usually whatever caliber I'm shooting at the time. :kidding::kidding:

(Either that or I only hit the target once...)

[rintinglen]

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.

I laughed out loud at this comment. How True!