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Old May 28, 2013, 10:38 AM   #1
Jay24bal
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Measuring Groups

I am brand-spankin new to precision shooting with a rifle, and have a question about group measuring. I see two methods people use to measure groups and was wondering which is correct and which is used in competitions?

1. Measure outside to outside of holes

or

2. Measure outside to outside of holes then subtract the diameter of the bullet

I have been doing some testing of loads for my .223 Rem and have found a good load. At 100 yards, I measured a 5-shot group by going outside to outside (not subtracting .224) and got .6815 inches. So is my group size .6815 or .4575 (.6815 - .224)?

Thanks in advance. I just want to know how close I am getting to some of the numbers I see from competitions.
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Old May 28, 2013, 12:08 PM   #2
Jim Watson
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Your official group size is .4575, groups are measured nominally center to center of the two widest shots so caliber does not affect the quality.
But it is hard to locate the center of the hole so outside to outside minus one bullet diameter works.

If I am shooting far enough or with a gun of only moderate accuracy and not getting "one ragged hole" I just measure from the outside of one wide hole to the inside of the other. But an accurate enough rifle won't leave clear individual holes at 100 yards and maybe even more.
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Old May 28, 2013, 12:35 PM   #3
Jay24bal
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Thanks Jim

Thanks for the reply, this is what I was looking for, and also what I assumed to be the case.

Hopefully I will get to one ragged hole down the road, but for now I can live with my group considering it is my first attempt at hand loading rifle rounds and the quality of the gun (stock Savage Axis with Barska glass). I want to play around and learn the ropes before I go searching for high end guns. I have no aspirations of being a bench rest shooter, just want to be able to squeeze every bit of accuracy out of the rifles I have. Time to tinker with my other 223 and other rifles now!

Thanks again.
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Old May 30, 2013, 05:36 AM   #4
WESHOOT2
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Datsa a great group!
Really.
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Old May 30, 2013, 08:10 AM   #5
Brian Pfleuger
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Check out the free version of OnTarget. It's got a bit of a learning curve but it sure makes the measurements easy.
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Old May 30, 2013, 08:21 AM   #6
Jay24bal
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OnTarget

Brian -

I am at work for the day, and they will probably frown upon me downloading it to the company laptop, but I did go to their site and see what it is all about.

As I have not downloaded it to play with, I am not aware of all the features. What other features does it have beyond group measuring that you have found helpful?

Thanks.
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Old May 30, 2013, 11:21 AM   #7
Brian Pfleuger
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Measuring Groups

None.

That's what it does, measures groups. It just does it very accurately if you enter the data correctly.

It has other info about the group too, besides just size. Standard Deviation and some other things, I think. Mainly, it's a good, consistent way to measure groups.
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Old May 30, 2013, 08:39 PM   #8
Jay24bal
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Thanks

Thanks Brian. Until I get to the point where statistical analysis and precision down to the hundreth is required, my calibers I use for reloading will do the job for me.

I do appreciate the responses as I always assumed it was a center-to-center measurement.
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Old June 8, 2013, 10:07 PM   #9
Bart B.
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A side note, in Great Britain, the standard is across outside edges of the two widest shots. They don't subtract bullet diameter; that's just a number that isn't used. But they do well with it as it works for them.
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Old June 9, 2013, 02:14 PM   #10
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You'd think it would be argued that one should go from inside edge to inside edge, as that's what counts when they touch a scoring ring. I suspect people shooting small groups would object to the negative numbers they would occasionally get, though.
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