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Old 09-14-2019, 07:50 PM
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Measuring Group Size



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if you measure groups edge to edge instead of c to c, is bullet diameter the best you can do?
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Old 09-14-2019, 08:35 PM
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Cuzz, the smallest measurement possible would be whatever size bullet u r shooting. If it is measured edge to edge. Example a 30cal can't be below.308 because that's the diameter of the bullet.
Sorry if this isn't what you were asking.
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Old 09-14-2019, 08:37 PM
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Originally Posted by Ett2 View Post
Cuzz, the smallest measurement possible would be whatever size bullet u r shooting. If it is measured edge to edge. Example a 30cal can't be below.308 because that's the diameter of the bullet.
Sorry if this isn't what you were asking.
But remember to take into account that the hole in the paper may not be the same as bullet diameter. It can vary depending on the type of paper and the target backing. Shoot one hole somewhere on the target and measure that to get your base.
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Old 09-15-2019, 05:38 PM
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Cuzz, the smallest measurement possible would be whatever size bullet u r shooting. If it is measured edge to edge. Example a 30cal can't be below.308 because that's the diameter of the bullet.
Sorry if this isn't what you were asking.
thats what i was asking and what i thought, i was just making sure. Ive always measured c to c .
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Old 09-15-2019, 05:50 PM
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Originally Posted by Ett2 View Post
Cuzz, the smallest measurement possible would be whatever size bullet u r shooting. If it is measured edge to edge. Example a 30cal can't be below.308 because that's the diameter of the bullet.
Sorry if this isn't what you were asking.
Sorry but that is wrong. You measure center to center or outer edge and then subtract the diameter of the bullet. If you shot 5 shots from a .308 into a single hole the group size is not .308. You measure edge to edge and subtract the bullet diameter so it would be a .0" group. That's an extreme example but done for effect. Bottom line is you can have smaller than .308" sized group shot with a .308.
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Old 09-15-2019, 10:09 PM
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Sorry but that is wrong. You measure center to center or outer edge and then subtract the diameter of the bullet. If you shot 5 shots from a .308 into a single hole the group size is not .308. You measure edge to edge and subtract the bullet diameter so it would be a .0" group. That's an extreme example but done for effect. Bottom line is you can have smaller than .308" sized group shot with a .308.
I think the confusion here is oto compared to ctc if measured 5-shots oto using your example it would be .308

now to see the group size ctc , you would then subtract .308 to get each shot's center from each other, again using your example .308 -.308 = 0.000 ctc
so yes you can get a smaller group, in a sense if looking for ctc but outside to outside would be whatever the bullet holes were.

Lee
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Old 09-16-2019, 02:15 AM
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Extreme outside to outside minus bullet diameter. This is how BR matches are judges for smallest groups. No deal about the hole the bullet makes in the paper. For rimfire, its extreme outside to outside, minus .223. For center fire, its extreme outside to outside minus factory bullet diameter.

The hole in the paper thing... RFC was the first place I ever heard that.
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Old 09-16-2019, 06:27 AM
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Only at RFC

As Sophia said , the paper can make bullet holes seem smaller



Lee
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Old 09-16-2019, 09:54 AM
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At benchrest for group matches the Neil Jones device is usually used. Even with that, if there is any doubt about who won, each target is measured three times and the average used for the group size.

Ref: Neil Jones Device.Neil Jones Measuring Device.

There is a computer program called On Target that is every bit as accurate as the Neil Jones measuring device. It's can be downloaded for free.

Ref: On Target
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Old 09-16-2019, 05:02 PM
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I find that the bullet holes are generally smaller than the caliber for .22LR simply because the velocity of the bullets are so low.

This is not very scientific but this is what I have discovered using On Target Software to measure groups.
With On Target you choose a caliber sized circle to match the edges.

Interestingly, for a .22 LR the best circle that matches the outside of the ring on the paper is 0.177 even though the bullet diameter is 0.224.
For a .223 Remington also with a 0.224 bullet, the best circle is 0.204 because the bullet velocity is more than 2x the velocity of a .22LR.
And a .22-250 that is about 500 fps faster than a .223, using the same .224 bullets, the best circle is actually a 0.224 circle.

It could be that the faster bullet just blows the paper apart and the slow bullets let it slide around the bullet and regain some of its shape.
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Old 09-16-2019, 06:30 PM
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Originally Posted by Rimfire5 View Post

It could be that the faster bullet just blows the paper apart and the slow bullets let it slide around the bullet and regain some of its shape.
When I shoot groups for the games here on RFC I shoot 4 single shots for sizers. I then measure each one , add them and divide by 4. That gives an average sizer.

When doing so my CZ455 Varmint usually has a .212 sizer.
My GM HT 10/22 shoots a .215-.216
My Kidd barreled 10/22 shoots a .214
All shot with the same ammo.
It depends on the choke and bore of the barrel that you are swaging a hot piece of lead through.
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Old 09-16-2019, 08:57 PM
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https://www.youtube.com/watch?v=e_QS_UfbpQs
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Old 09-17-2019, 01:50 PM
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Originally Posted by Hi-NV Shooter View Post
I think the confusion here is oto compared to ctc if measured 5-shots oto using your example it would be .308

now to see the group size ctc , you would then subtract .308 to get each shot's center from each other, again using your example .308 -.308 = 0.000 ctc
so yes you can get a smaller group, in a sense if looking for ctc but outside to outside would be whatever the bullet holes were.

Lee
No confusion on my part. Just trying to clarify it for him. No one measure just OTO. That is not a proper representation of group size.
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Old 09-17-2019, 03:30 PM
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Estimating the center of a hole is not that difficult. I find it plenty accurate for government work. For my own 2c, I feel like I can judge the center of a bullet hole better than the outer edge. Obviously opinions vary as does the circumstance where extreme accuracy in measurement it needed.

Oh , I get it, sometimes the hole is one big hole and centers cannot be seen. Yea, I am usually so happy to see that, I am not sweating the size. Then like Sophia said.

Last edited by fourbore; 09-17-2019 at 03:32 PM.
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Old 09-17-2019, 07:44 PM
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No confusion on my part. Just trying to clarify it for him. No one measure just OTO. That is not a proper representation of group size.
Well if you test ammo like I do, oto is what matters. and I know Lapua and Eley use outside measurements when they lot test a rifle.


Center to center sounds real good and impressive, but outside to outside is more real world, for example 11mm -5.6mm= 5.4mm sounds real small, but I know it is still 11mm in size or .433 of an inch

Lee
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