Center to center or all inclusive

baitpile

baitpile

Active member
...on measuring group size? I'm the guy that has to have the entire round contained inside the measured circle. I know lots of guys, maybe most, measure center to center. I know scoring targets, if it breaks the line it counts. But, in load work up or really wringing out a gun, I like to have the entire round contained inside the measured group. What do most do/like? What is the standard? We all see lots of group "sizes" posted. Just curious.
 
Unless shooting for money, it doesn’t really matter. Keeping them inside of the MOA target is always my objective. 1/2 or 1/4 of that is even better.
 
Originally Posted By: pahntr760Unless shooting for money, it doesn’t really matter.

there you go boys and girls. unless there is a dollar at stake don't even bother measuring those groups.
 
Personally i go center to center. But if you go edge to edge thats fine just so long as you make note of it for your records. I just try to stick with something and not change it mid stream. I just happen to choose center to center. Mainly because thats what most people refer to.
 
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Originally Posted By: pahntr760Unless shooting for money, it doesn’t really matter.

Yup.

If it is for money, it's C-T-C.

I mostly just ignore any group sizes anyone talks about on the internet. Most of the pictures I see with group sizes written on them that are, well, let's just say, generous. When you have two .243 bullet holes just perfectly touching on the edges, that's a .243 CTC group, so when there is a fair amount of paper between the holes, I'm not sure how that becomes a .210 group
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Then there's 3 shots vs. 5, one group out of however many vs. an honest average. Etc., etc.

We ain't all speaking the same language. So I mostly just tune out any talk of group sizes as meaningless noise.

Especially since, as has been said, it just doesn't matter.

- DAA
 
Originally Posted By: baitpile...on measuring group size? I'm the guy that has to have the entire round contained inside the measured circle. I know lots of guys, maybe most, measure center to center. I know scoring targets, if it breaks the line it counts. But, in load work up or really wringing out a gun, I like to have the entire round contained inside the measured group. What do most do/like? What is the standard? We all see lots of group "sizes" posted. Just curious.

It doesnt really matter what you "like." Group size is a commonly accepted measurement method, which is center to center.
 
i measure my groups with On-Target, and go by the Center to center from that.


as others have noted - for load developement purposes it really doesnt matter..... as long as you're CONSISTENT with how you're measuring.

we shoot for consistency, so you have to measure consistently too to have useful data.
 
Measuring outside edges -bullet diameter gives you center to center, actual group size. Debating between the 2 is like arguing 6 vs half a dozen.
 
Originally Posted By: NdIndyMeasuring outside edges -bullet diameter gives you center to center, actual group size. Debating between the 2 is like arguing 6 vs half a dozen.

Very true, but unless you have one of those bench rest measuring devices, you could miss your EXACT group size by a couple thousandths of an inch!
 
Thanks guys, just as I suspected!!
Quote:So I mostly just tune out any talk of group sizes as meaningless noise.

Especially since, as has been said, it just doesn't matter.
I have to agree with DAA...most group size discussion is just noise!!

Quote:as long as you're CONSISTENT with how you're measuring.

we shoot for consistency, so you have to measure consistently too to have useful data.
And Plant.One hit it on the head as well..."consistency" for data is the important issue for that data to mean anything!!!
I was just curious for a mid summer discussion.
Carry on.
 
1. Center to center
2. Most internet groups are bs
3. 3 shot groups indicate very little. Barrels that I consider junk and would not hunt with will still put 3 nearly touching. Up groups to five shots and in those barrels flyers always show up.
 
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Why won't you hunt with a gun that puts 3 nearly touching? Are we talking coyotes, big game?

Originally Posted By: varminter .2231. Center to center
2. Most internet groups are bs
3. 3 shot groups indicate very little. Barrels that I consider junk and would not hunt with will still put 3 nearly touching. Up groups to five shots and in those barrels flyers always show up.
 
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One thing that most people will agree with is that "internet groups" are usually stated as being far smaller than they actually are if measured properly.

Without a good instrument (not just a simple caliper) to actually determine groups size C_T_C, they are at best a WAG as determining a bullet hole center point is also a wag without special tools to do it.

Here is a pretty good technical discussion about measuring group sizes that talks about both C_T_C and outside edge groups. It may take some re-reading as its strung out as most internet posts become when two or more people disagree on something. In this case the two opposing views come from people who knows their stuff versus the occasional internet expert who can't believe he might be wrong in spite of empirical evidence to the contrary.
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http://www.benchrest.com/archive/index.php/t-55613.html

Here is a search page with a lot more discussion.

https://duckduckgo.com/?q=measuring+bench+rest+groups&t=ffab&atb=v106-3_f&ia=web

The bottom line is that any internet group measured with a simple caliper using either method to determine groups size probably wouldn't fly at a sanctioned shoot using the proper tools.

The name of the device widely used in sanctioned shoots escapes me at this moment, but maybe discussions at one of the other links will mention the name. Simply stated, it has a target measuring caliper that is fitted with a plexiglas plate that has several circles conforming to the diameter of commonly used target bullets and their resulting holes sizes on sanctioned target paper.

Consistency in measurements from one shoot on the west coast to another on the east coast on the same day is paramount in procedures used in sanctioned shoots. Same same for the amateurs doing it to get an approximation of a group size to impress their friends on the internet.
 
Calipers are just the best tool available to most of us. Neil Jones makes a magnifier set up that is used in many matches for measurement using a mic.

I measure them looking for consistency and to see if there is any gross variation from group to group. Eyeballing is fine but eyeball and comparing a 17 caliber vs a 45 and the results are quite spectacular on ones psyche. I need visual feedback down the road as the memory is not so good after shooting 15-30 groups in load testing. Just like guys don't believe in using chronographs during initial load development to me it's a tool to provide a data point.

No one has to care if it's dead nuts but when you see a pair over lap and you are shooting a 243 you no darn well the distance CTC is less than 243. It's nice to know approximately how much. I don't like close enough in my life. I avoid three shot groups in most instances and ultimately given the real world it's the first shot that counts, or should, in most applications we deal with. In my previous life that was the one I had to teach the kids but for now I just apply it to PD's.

Greg

 
Consistently and accurately measuring groups more than well enough for personal record keeping and data analysis is very easily achievable with a simple vernier caliper. Even a Harbor Fright plastic one.

None of this matters. It really, really doesn't.

But I'll mention anyway...

A lot of talk about subtracting bullet diameter. This usually gives you a measurement smaller than the actual group size. On some paper, quite a bit smaller.

Target tag is made specifically to not stretch and cut a true hole. But it's expensive. Targets printed on it aren't cheap.

If, like me, you mostly use targets you printed yourself, on the cheapest paper Walmart had, or the cheapest preprinted targets you could find, the paper they are printed on is most likely going to stretch a bit as a bullet passes through it. I've seen some paper that stretched so much that a .22 made holes that looked like a .17. I think humidity might even have an effect.

But, so, anyway, the point... If the paper is stretching the holes will be smaller than bullet diameter. If the holes are smaller than bullet diameter and they probably are, subtracting a full bullet diameter from the outside edges will give you an incorrect group size that is smaller than actual C-T-C.

Two simple ways to avoid this error. If you have separate bullet holes, measure the bullet holes and subtract that from the outside edge measurement. I have seen some pretty extreme cases with some of the cheapazz copy paper I usually use. Like .22-250 holes that measure .180 and .17's that measure .14. Or, again if you have separate bullet holes, just measure from inside edge to outside edge of the widest shots. Up to you to decide what the "edge" is, but if you do it very much you'll get quite consistent with it.

For a bug hole without a lone bullet hole, find a lone bullet hole or make one. Measure it. Subtract from the outside edges of the bug hole.

- DAA
 
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