Question.... How to measure groups.

[NDAR15MAN]

I am sure this question has been asked before but how do you shooters measure a group size of let’s say 5 shots ? Do you measure from inside bullet hole to inside bullet hole or the out side to outside on the bullet holes thanks. MD

 

[Ned Ludd]

Bullet holes in paper are typically smaller than bullet diameter; the hole shrinks after the bullet has passed through. For that reason, I used to do center-to-center measurements back in the day, because measuring outside to outside and subtracting a bullet diameter would technically return a value that is slightly smaller than the true value, even though accurate center-to-center measurements with calipers are slightly more difficult to make. Nonetheless, either method will work.

The real question is whether any variance between the two methods is enough to even make a noticeable difference? Probably not. Is a 0.28 MOA group really any different than a 0.27 MOA group? The differences between the two methods would be small, although not zero. More importantly, why would you be manually measuring groups in this day and age where good shooting programs such as On Target are available as shareware or freeware? Scan or photograph the target image with an internal reference distance (i.e. ruler) and let the software estimate the groups for you.

 

[Straightshooter1]

I am sure this question has been asked before but how do you shooters measure a group size of let’s say 5 shots ? Do you measure from inside bullet hole to inside bullet hole or the out side to outside on the bullet holes thanks. MD

I take my caliper and zero it on the bullet diameter, then measure outside to outside. Since the caliper is zeroed on the bullet, the reading on the caliper has the bullet diameter already subtracted. And as Ned Ludd says, the minute difference in measuring center to center doesn't really matter . . . unless you're measuring in competition.

 

[AlNyhus]

The correct way is to measure the diameter of a single bullet hole in the target paper and use that as the 'standard'.

Let's say a .224 bullet makes a .206 diameter hole. Measure your group outside to outside and subtract .206 for the correct group size. Type of paper and backer all make a difference.

Here's an example...the .308 bullet made a .290 hole in the paper so .290 was the 'standard' to measure the group size:

 

[NorCalMikie]

Outside to outside then subtract the bullet size.
My best 5 shot group with a .221 Fireball is .110.
And if they're all going in the same hole, don't bother to measure.
Just frame it and hang it.

 

[AlNyhus]

Outside to outside then subtract the bullet size.

Commonly done but technically incorrect. -Al

 

[NDAR15MAN]

Guys thanks for the info. I do not shoot competition or reload. I do keep all my targets when I am sighting in a new gun and test out factory ammo. Don’t know why I did not think the honest and the simplest for me would be to measure middle of hole to middle of hole.
Thanks. Again. MD

 

[STOMP442]

Get the ballistic X app. Its cheap and super easy to use and will give you precise accurate readings.

 

[grovey]

I usually measure the extreme out to out of the "marked" holes, and then add 0.010 before subtracting the diameter of the bullet. Maybe that's not quite enough.

 

[CaptainMal]

The correct way is to measure the diameter of a single bullet hole in the target paper and use that as the 'standard'.

Let's say a .224 bullet makes a .206 diameter hole. Measure your group outside to outside and subtract .206 for the correct group size. Type of paper and backer all make a difference.

Here's an example...the .308 bullet made a .290 hole in the paper so .290 was the 'standard' to measure the group size:

Just did some targets done during the Manatee Florida IBS Championship last seek. .221 seemed to be the paper hole size for my .243 bullets. Did outside to outside and got within .01" of the "official" measurements from that shoot.

This sure seems to work. Thanks.

 

[NorCalMikie]

Commonly done but technically incorrect. -Al

I AM technically incorrect.

Get the ballistic X app. Its cheap and super easy to use and will give you precise accurate readings.

So, now I need to get a smart phone too?? Will it never end?

 

[MGYSGT]

Center to Center is way close enough for me.

 

[Tim Singleton]

Best to measure a single bullet hole and subtract

An in tune gun makes a little bitty hole that is why official group match score keeper check each target and subtract form outside to outside

 

[CaptainMal]

That brings up the issue of bullet yaw. Seems that not always are bullets coming from an "in tune" rifle. Then the wind gusts and blows things sideways causing a meplat hole to be on the side of a bullet hole. Then the entire outside marking is not circular but ovular. Also, the holes inside that mark are often torn sideways. I know about that after dealing with scoring things like that where it is only one strike but the tear is not circular and tricks you to thinking it might be two shots close.

When the strikes are not circular due to yaw, no matter the cause, the size of the mark is not the same for all shots. Then, to take a measure of that hole mark size and subtract from an outside to outside measure, might not be all that accurate and repeatable.

 

[unkie716]

That brings up the issue of bullet yaw. Seems that not always are bullets coming from an "in tune" rifle. Then the wind gusts and blows things sideways causing a meplat hole to be on the side of a bullet hole. Then the entire outside marking is not circular but ovular. Also, the holes inside that mark are often torn sideways. I know about that after dealing with scoring things like that where it is only one strike but the tear is not circular and tricks you to thinking it might be two shots close.

When the strikes are not circular due to yaw, no matter the cause, the size of the mark is not the same for all shots. Then, to take a measure of that hole mark size and subtract from an outside to outside measure, might not be all that accurate and repeatable.

Sir, please use the above hypothetical and explain to the Accurate Shooter nation how you and the other gentleman made the decision to DQ the attached target from your most recent match. Thanks in advance.

 

[JEFFPPC]

SPJ, which shot do you call a double? It would be nice to see this target from the rear. I would call the 12:00 ten as possible.

 

[NorCalMikie]

If they're all going in the same hole, no need to measure.

 

[CaptainMal]

The meplat holes are off center. That shows bullets were yawing into the target and tearing the center holes at different sizes and angles.

The center one has a blue paper pushed into the center from the 1 o'clock position. The top left one has it pushed from left to right. The top right one is from 7 o'clock and in. The lower left one is from 10 o'clock and in.

All the holes seem to be the same size, slightly ovular and are cut at different angles into the target. If I remember correctly, and yes I acknowledge, my memory is faulty, the back of the targets showed nothing unusual except for the different angles of each entry.

The IBS has seen and examined these pictures. Jim Bauer responded to me on this picture. Contact him for that information.

 

[unkie716]

Here is the back side of the above target as requested. Please understand that quite a few people have poked and prodded at the hole formed at 11:30 in the ten ring which probably alters it somewhat. I will say that everyone interested enough to look at the target went straight to that hole which would lead one to think that something appeared different about it. If possible, please view the front view above with a smart device and use your thumb and forefinger to pan open the hole and see what you think.

 

[CaptainMal]

This target was one of four the Manatee scoring team had to deal with in just one weekend shoot at 600 yards. I was part of the judging team called in to render an opinion. Don't remember my particular decision but do remember that I personally had a different opinion than the other two judges on two of the decisions. Later found out the official scorer had the same decisions as I did. None of that is important other than to say these decisions are very difficult for a variety of reasons.

Since the shoot I have spent more time discussing this with three IBS officials. I have emphasized that things like this seem to be happening quite often to us. Others at the shoot spoke to me about noting this issue at other shoots around the country. Because of that I have proposed to the IBS possible solutions. Have not received any notification of any decisions on this yet. Maybe some inquiry from other shooters would be useful to them?

I have firmly asked that in the absence of definitive proof there are the correct number of shots in the target AND the shooter swears they did not experience any mechanical issues they are aware of and no mitigating evidence, that shooter be allowed to shoot the target over.

To me it is a sorry state when hideous bad luck has a good shooter make a perfect entry in another hole and is punished for it with no recourse.

Starting at a club shoot this March we are going to experiment with various ways of creating some kind of backing paper behind the main target and see if that could work. Having sighter plates close behind may make splatter tears so bad it will not work but we are trying

It bothers me that this situation exists with no recourse to verify shots fired and impacts received. Hope it bothers others as right now there is no way to deal with this. In the future it will be difficult to find people who would volunteer for the trauma of having to make a decision that could negatively impact good shooters who have bad luck. Being hinted of incompetence and senility, no matter if correct or not, is not a pleasant experience. Even hints of prejudice in scoring add to the displeasure of being a scoring judge. I think there needs to be a reasonable out. That's why I proposed a "shoot over" addition to the IBS rule book for consideration in the future.