which is better for determining whether load A or load B is more accurate?

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harleyrock posted this 23 January 2019

To determine which is significantly more accurate of two loads which is better:

One 20 shot group, or

Two 10 shot groups, or

Four 5 shot groups?

I know more is better (sometimes), 100 shots, however you bunch them, is better than 20, but there comes a point of dimensioning returns when it comes to hunting or plinking loads.

Tom Stone

Lifetime NRA since 1956, NRA Benefactor, USN Member, CBA Member

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M3 Mitch posted this 23 January 2019

I read somewhere that 7 shot groups give the best bang for the buck. 

I'd like to add a question about how many groups at a certain percentage smaller actually represent a statistically defensible "better" level of accuracy. 

Pretty sure I have a statistics book on the shelf that has the answer, but am too lazy to dig it up.  At least I am honest.

Something else to think about is group shape.  If the group is not round, I think in general that means "something else" is wrong - bedding, scope mounting, bad technique, etc.

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RicinYakima posted this 23 January 2019

Please use the "search" function. There are literally hundreds of posts and opinions on this subject. Thanks, don't want to start the big fight again.

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M3 Mitch posted this 24 January 2019

http://www.the-long-family.com/Group%20size%20statistical%20analysis.pdf

 

This is a pretty clear write-up.  I don't see how anyone can argue about this, it's simple math. 

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joeb33050 posted this 24 January 2019

 

8 SHOTS PER GROUP

 

When we shoot groups to estimate the long-term-accuracy of a load, there is a precision of that estimate. That precision is expressed, (example), thus: “Based on the test, we are 95% sure that the long-term-accuracy of the load is .94” +/- 14%”.

 

We see 10 or 5 or 3 shot groups reported; and advocates staunchly defending their choice of shots per group.

 

After analysis, I find that there is no practical difference between estimate precision and the number of shots per group.

 

Shots per group doesn’t matter.

 

The total number of shots fired in a test does matter; a lot.

 

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Larry Gibson posted this 24 January 2019

Depends on the type of shooting you are going to do.  My own experience indicates if you are hunting then 3 or 5 five shot groups allowing the barrel to completely cool between groups and cleaning or not depending on how you hunt with it between groups will give the best idea of the accuracy capability of the load.

If you are shooting a match then the number of shots in a relay plus sighters is the best number to use for accuracy testing.

If just accuracy testing a load then 8 shots is the minimum, as joe mentions, to give an indication.  My own method is to use 8 - 10 shots to initially get an idea and then shoot three 10 shot groups (letting the barrel cool completely and or clean it) to confirm the accuracy potential of a load.  I have seen to many anomalies of 8- 10 shot groups "looking good" with the first test only to actually prove worse and/or inaccurate in later use.

LMG

Concealment is not cover.........

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harleyrock posted this 24 January 2019

 

8 SHOTS PER GROUP

 

When we shoot groups to estimate the long-term-accuracy of a load, there is a precision of that estimate. That precision is expressed, (example), thus: “Based on the test, we are 95% sure that the long-term-accuracy of the load is .94” +/- 14%”.

 

We see 10 or 5 or 3 shot groups reported; and advocates staunchly defending their choice of shots per group.

 

After analysis, I find that there is no practical difference between estimate precision and the number of shots per group.

 

Shots per group doesn’t matter.

 

The total number of shots fired in a test does matter; a lot.

 

So I may as well shoot 20 shot groups of each load?  

I was thinking 5 shots alternating, e.g.  5 shots of load "A" at target "A " followed by 5 shots of load "B" at target "B"  until both targets would have 20 shots.  The alternating would average out "barrel condition".

Are you saying, joeb, that 8 shots per group would be just as good as 10 or 20 shots per group?

Lifetime NRA since 1956, NRA Benefactor, USN Member, CBA Member

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joeb33050 posted this 24 January 2019

 

So I may as well shoot 20 shot groups of each load?

Sure, 20 X 1 or 10 X 2 or 5 X 4 or 4 X 5 or 2 X 10---it doesn't matter.

There is a discrete amount of information in each shot/hole. For a given number of total shots, like 20, how you divide them up doesn't change the amount of information. Nor does what is embroidered on your hat, or where you went to high school, or your favorite number of shots per group. The only way to get more informat5ion is to fire more shots. 

 

I was thinking 5 shots alternating, e.g.  5 shots of load "A" at target "A " followed by 5 shots of load "B" at target "B"  until both targets would have 20 shots.  The alternating would average out "barrel condition".

Are you saying, joeb, that 8 shots per group would be just as good as 10 or 20 shots per group?

No, the 8 marks the 8th stats/groups topic on the list I've posted here too many times. 

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OU812 posted this 25 January 2019

I like four 5 shot groups from a hot barrel. Groups that shift is not good.

When developing accurate load, a 3 shot groups will tell you quickly.

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harleyrock posted this 31 January 2019

John Alexander referred me to an article he wrote in TFS on this subject and that was the best explanation I have seen. So as the OP, the issue is solved.  Thank you all for your thoughtful replies.

 

Tom Stone

Lifetime NRA since 1956, NRA Benefactor, USN Member, CBA Member

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JeffinNZ posted this 01 February 2019

I would be inclined to think 5 x 5 shot groups with each target laid exactly over the same backer each time thus creating a backer with a 25 shot group in the end. 

Cheers from New Zealand

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