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Correct way to measure a group?

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#1
10-17-2005, 01:52 AM
 Silver Member Join Date: Mar 2005 Location: Australia Posts: 177
Correct way to measure a group?

What is the correct way to measure a group centre to centre?
Can someone post a picture example of measuring a group using verniers, would be appreciated.

Thanks

Cheers
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skip
#2
10-17-2005, 06:41 AM
 Gold Member Join Date: Oct 2004 Location: Northamptonshire England Posts: 676
Re: Correct way to measure a group?

Skip,
From an ex benchrest shooter:
Identify the edges of your group that are furthest apart and draw a line through the centre of the opposing bullet holes. Set your Vernier on the group so that the edges of the blade form a 90 degree angle with the scribed line at the furthermost edge and take a reading.
Record this reading and subtract your bullet diameter, this will give you your C-C group.
If you want to, divide by 1.09 to get MOA.
Hope the pix will help explain.

My 243 Group.

308 Group

Ian.

"I meant to shoot the pike but the duck got in the way"
#3
10-17-2005, 08:48 AM
 Silver Member Join Date: May 2005 Location: Bozeman, MT Posts: 241
Re: Correct way to measure a group?

I am far from an expert on this subject, but I'm sure that I have read that the holes left in paper targets are usually a little bit smaller than the caliber size. If this were true, it would make groups measured using this method prone to being slightly smaller than they actually are. The amount of effect this would have on relative group size (that is percentage) should increase as the group size decreaes. That is, on a 2" group a .1" error would make much less difference than on a .2" group. I've heard of actually measureing the centers of the bullet holes, however, I don't know of any superior way to do this.
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Empirical results rule!
#4
10-19-2005, 01:01 AM
 Silver Member Join Date: Jan 2004 Location: Mississippi Posts: 182
Re: Correct way to measure a group?

I measure outside to outside on the farthest bullet holes, then subtract the bullet diameter. This will give the same result as measuring center to center.
#5
10-19-2005, 01:03 AM
 Silver Member Join Date: Mar 2005 Location: Australia Posts: 177
Re: Correct way to measure a group?

Thanks all, now I know how to do it 'properly'

Cheers
__________________
skip
#6
10-19-2005, 08:53 AM
 Silver Member Join Date: Mar 2002 Location: Prince George British Columbia Posts: 128
Re: Correct way to measure a group?

Now that depends also on where you are when the group is discussed. In comp. and at the range we measure the group outside to outside then subtract caliber. Later when talking about group sizes in the bar knocking back some cold ones the usual accepted practise is to automaticly eliminate the flyer, measure the remaining bullets then subtract the largest caliber you have at home. Also dont forget that the distance the group was shot at must be multiplied by 1.5
#7
10-19-2005, 09:10 AM
 Platinum Member Join Date: Jun 2001 Location: Potomac River Posts: 5,088
Re: Correct way to measure a group?

One thing that will help your group size is to take your target to work and put it in the copying machine and set the machine for 50% reduction. [img]/ubbthreads/images/graemlins/grin.gif[/img] Sometimes, if I am having a bad day I have to use more than 50% reduction [img]/ubbthreads/images/graemlins/blush.gif[/img]
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