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:

 

[JFrank]

We just measure center to center and skip all the other stuff simply because not everyone has the same caliber rifle

 

[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.

 

[JFrank]

Looks like 5 shots to me

 

[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.

 

[JFrank]

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.

Me too