# best method for measuring a 3 shot group

Discussion in 'Long Range Hunting & Shooting' started by walserjack, Jul 27, 2011.

1. ### walserjackMember

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I was told to use calipers and measure from outside to outside of farthest holes and then subtract the caliber. In my case it is a 308. Using this method I shot a .26 with HSM Berger 168 gr and .27 with Federal premium Sierra Gameking 165 gr and a 5 shot .70 with VLD. All at 100 yards. Is this method correct?

2. ### mike33Well-Known Member

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Re-measure you just 3 set world records. Outside to outside - bullet diameter = group. .260, .270, and .700 sounds more like it though.
mike

3. ### Browninglover1Well-Known Member

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If you read... he did say what his group sizes were. He doesn't need to add a "0" on the end. .26 is the same thing as .260 So yes Walserjack you are correct and excellent shooting on those 1/4 inch groups.

4. ### mike33Well-Known Member

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I think you should add the zero, i used to shoot br in the 90's and a .99 and under was a screamer at 100 yards

5. ### Browninglover1Well-Known Member

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The added zero would be more common because everything is measured in thousands of an inch (the third place after the decimal)

However it's been long enough since you've shot bench rest that you've forgot how to read ha ha . A .99 inch group is only 10 thousands of an inch away from an inch and won't win any competitions at all. A .099 inch group is outstanding and that is what I'm assuming you meant to type. You're just missing where he's putting the decimal (and you placed it incorrectly in your other example). Mathematically he's 100 percent correct.

I don't mean to start a fight or sound like a jerk, he could add the zero because it is more common, but he does not need to. And again... you missed a decimal place or maybe even two by saying that a .99 inch group was a screamer. .099 would be a screamer and .009 is basically one hole and I have no idea how they can measure a tear in paper to that kind of precision and accuracy.

6. ### mike33Well-Known Member

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With you. Saying im old, LOL. I first seen the 26 and so on and though wow how did you measure that or i want that gun even though i dislike 308. I just always go 3 digit.
mike

7. ### WildRoseWell-Known Member

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Take very, very, very good care of that rifle. You may never get another one that shoots this well.

8. ### Browninglover1Well-Known Member

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At least you only made the mistake on an internet forum

I once made the same mistake when checking a part for one of our machinists and it cost the company a little bit more money than they were wanting to lose. hahaha I learned my lesson and have really watched the decimal place since.

And I agree that 3 numbers is just easier to understand because everything is being measured to the thousands place. By the way if you ever shoot a gun that shoots .026 groups give me a call and let me come shoot it too!

9. ### mike33Well-Known Member

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Just dont wait by the phone to long.

10. ### walserjackMember

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Wow! Im suprised you guys think that I shot so well. I was a little suprised that it shot both the vld and game king so well. I have a Rem. mdl 700 sps tactical 308 with a Ziess Rapid Z 600 reticle. Very sweet gun and I set the trigger as light as I could. Dangerously light. Its the best gun Ive ever had. Keep in mind that these groups were shot of a shooting sled. More gun than shooter. One thing confuses me though, If you measure outside to outside then subtract the caliber how do you get a group that is less than the bullet diameter? The shots were touching but its not like they all went in the same hole

11. ### edgeWell-Known Member

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Actually IMO, two decimal places would be preferred unless you had a precision way to find the centers....and hand held calipers measuring a ragged paper hole don't get you there!

By showing two decimal places you are acknowledging a lesser precision.

As a side note, engineers with no machining experience will often dimension holes to four digits when they only need a clearance hole. Depending on the print tolerances you would normally need to hold a 4 decimal hole into the ten thousandths of an inch whereas a clearance hole may only need to be held to several 0.001's or even 1/64 of an inch.

edge.

12. ### Browninglover1Well-Known Member

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What you are doing by measuring properly is finding out how far away the bullets landed from each other center to center. This means if a perfect world you could shoot a 0" group with whatever caliber you wanted as long as all the bullets went in the same hole. A .26" group means that your bullets landed just barely over 1/4" inch apart center to center. Imagine if you shot a one hole group.... you would measure outside to outside and read .308, after you subtract bullet diameter you would end up with a .000 inch group. This means that every shot landed exactly the same place as the other.

In my experience people tend to think bigger rifles shoot tighter groups than they really do because the edges (inside edges in this example) of the bullet holes appear closer together. I had a guy at the range shooting his 308 that told me his gun was shooting lots better than my 22-250 because the holes looked closer together. However, after we measured his group he was shooting around .800" at 100 yards and my 22-250 was shooting around .650" and was clearly the winner.

That's why we measure center to center. Because it doesn't matter what caliber bullets you are shooting, it gives an accurate description of how far away your shots landed from each other.

Last edited: Jul 28, 2011
13. ### walserjackMember

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I went back and measured center to center. I found it to be easier to judge this way. My two best groups were vld at .40 and gameking at .42 Still good groups if you ask me. Thanks for the input. Although I was excited about the idea of a .26 group I would rather do it right.

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