Statistics and NRA accuracy testing.

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joeb33050 posted this 26 September 2018

 

 

 

 

Statistics and NRA accuracy testing.

 

The NRA most frequently tests accuracy with a set of five, 5-shot groups.

 

Group size, the accuracy measure, is the center distance between the two furthest-apart holes in the target, in each group.

 

With the assumption that shot location is distributed NORMAL, the ratio of largest group / smallest group has been calculated for both shots / group and number of groups per set.

 

For example, sets of five, 5-shot groups have the largest / smallest ratio  = 1.91, the average over many sets.

 

This ratio is due to random NORMAL variation alone, other effects such as wind and shooter ability would increase the ratio.

 

My center fire 5-shot average ratio for 121 sets of five, 5-shot groups is 1.97. The expected ratio is 1.91. Actual / expected = 1.97 / 1.91 = 1.03.

 

My rimfire 10-shot average ratio for 45 sets of ten, 5-shot groups is 2.69. The expected ratio is 2.42. Actual / expected = 2.69 / 2.42 = 1.11.

 

The Cast Bullet Association National Match results, 2015, 2016, 2017; sets of four, 5-shot groups, (rifle):

 

100 yards, 118 sets of four groups, actual ratio = 2.05, expected ratio = 1.77, actual / expected = 1.16.

 

200 yards, 115 sets of four groups, actual ratio = 1.98, expected ratio = 1.77, actual / expected = 1.11.

 

The NRA, American Rifleman, 198 sets of five group 5-shot tests ending in October 2018:

 

Pistol, 93 sets of five groups, actual ratio 1.61, expected ratio = 1.91, actual / expected = .84.

 

Pistol, 105 sets of five groups, actual ratio 1.58, expected ratio = 1.91, actual / expected = .84.

 

I can think of no reason that NRA actual / expected ratios would have a large-sample, (198), value LESS than 1; and can think of many reasons why it might be GREATER than 1.

 

I consider the NRA results to be suspect-perhaps false.

 

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RicinYakima posted this 26 September 2018

Thank you Joe.

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John Alexander posted this 26 September 2018

Interesting facts Joe.

Before the last move I had Am. Rifleman magazines back to 1952 and have always been interested in the ratio of smallest to largest group because it shows just how variable group sizes are.  What I found was there would be stretches of several years where the average ratio was very close to the expected 1.91. And other stretches, include the recent period, where the average ratio was consistently significantly less than 1.9 just as Joe has found.  The ratios I have tabulated have never averaged higher than 1.91.  This clearly shows that with some editors fudging goes on and always in the same direction of making the gun being tested look more consistent.

It isn't a federal crime, but it shows that some AR editors are susceptible to the temptation to fudge results a bit or disregard a big group, just like other shooters. The temptation to disregard results you don't like is hard to resist and part of human nature that some don't try very hard to resist.

John

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shake posted this 27 September 2018

I thought the NRA was the Gold Standard when it came to honesty and accuracy in the firearms publishing field. If this is true, where do we as members lay the blame? Mark Keefe? Should this be forwarded to the NRA for a reply?

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GP Idaho posted this 27 September 2018

While I'm not at the level of proficiency with by bench shooting as most of you competitive shooters may be, I do appreciate Joe including me as a recipient of his resent E-mail and his findings of interest. As to who we chose to trust for accurate information, I can't think of a better source than the results of CBA matches. Shots fired in a group setting and many witnesses.  Also, I can see where other organizations may have a financial reason to fudge the results.  I'm a little surprised  that the NRA would take the time away from their fund raising efforts to run tests at all. (Yes, I'm a NRA member) It makes me wonder if they rely on third party testing or just pull it out of their posterior..  Gp

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joeb33050 posted this 27 September 2018

I thought the NRA was the Gold Standard when it came to honesty and accuracy in the firearms publishing field. If this is true, where do we as members lay the blame? Mark Keefe? Should this be forwarded to the NRA for a reply?

I sent what' I posted here to a number of maybe-interested folks, and an NRA address. I'd like to send it to specific NRA tester folks, can't find addresses. Anyone?

 

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Scearcy posted this 27 September 2018

First Joe thank you for including me on your email list. Second I am not here to bash the NRA. I have also been a member for nearly 50 years. Their primary role now is as a powerful lobbyng group which requires money. Having said that, I would be happy to sign a petition encouraging them to devote a few more $ to some of their traditional activities. It would be nice to have a 2018 edition of the "NRA Handbook". We have a number of shooters here in the CBA that could contribute excellent articles to such a Handbook.

Jim

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joeb33050 posted this 28 September 2018

More data

 

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joeb33050 posted this 28 September 2018

and

 

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John Alexander posted this 28 September 2018

Joe,

I believe you have said that you don't use wind flags while shooting groups.

At the nationals the range is awash with wind flags.

Your group variation is quite close to the expected ratio.

Group variation at the CBA nationals is much larger than the expected ratio.

Therefore wind flags obviously cause more variation from group to group.

John

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Ken Campbell Iowa posted this 28 September 2018

... evil wind flags .... ha .... got me there .....

made my day ...

ken

oh, sounds like NRA members are just better shots ....

 

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joeb33050 posted this 29 September 2018

until SHE WAS 7 OR 8, ONE OF MY DAUGHTERS BELIEVED THAT THE SHAKING trees caused the wind. But, she never believed that shooting bullets in the order cast increased accuracy.

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Ken Campbell Iowa posted this 29 September 2018

...scary ... half the people on earth think the moon only appears at night ....   and think we are held on earth by the spinning of our planet ... thankfully, most of these types get harmlessly elected to public office ...

i do admit i am amazed at how God diverted rivers to run by large cities ...

ken

 

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