EXPERIMENT 1-SHOTS PER GROUP

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  • Last Post 12 September 2018
joeb33050 posted this 02 September 2018

We see 10 or 5 or 3 shot groups reported. The larger the number of shots per group, the smaller the number of groups-of data points. 100 shots will make 1 100-shot, 2 50-shot, 4 25-shot, 20 5-shot, and 50 2-shot groups.

Brent Danielson has long advocated the 2-shot group, giving the largest number of data points per total number of record shots fired.

We know that average group size varies with n = the number of shots per group, thus:

 If 2 shot groups size = 1; then

3 shot group size = 1.36

5 shot group size = 1.73

10 shot group size = 2.17

(The group size ratio for n >2 ~ n^1/3)

To test the use of 2-shot groups as a measure of accuracy, I will fire 6 5-shot groups and 15 2-shot groups.

The more of you who perform and report the results of this test, the more sure we will be of the results.

Test procedure/conditions:

Any gun that will reliably shoot 100-yard 5-shot groups <2" @ 100 yards. (I'll use a BSA Martini 12/15, 22 LR).

Range: 100 yards

Everything else is the shooter's choice-fouling shots, benchrest equipment, group measuring tools, targets, etc.

I will shoot my test tomorrow.

 

 

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stevebarrett posted this 02 September 2018

I wasn't aware of that relationship:  The group size ratio for n >2 ~ n^1/3

How is it derived?

Thanks

Steve

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joeb33050 posted this 02 September 2018

From 'A GROUP SIZE MODEL" , an excel workbook, that calculates group sizes for any average and stdev of X and Y; for groups from 2 to 10 shots. 

I'd be happy to send the workbook to anyone who wants it, and answer any questions.

 

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Ken Campbell Iowa posted this 02 September 2018

hey joe ... i got one for you  >>

i believe you have explained the relationship between (among? ) maximum group size ... and mean radius ..... relative to validity ...   over a large number of shots., the validity ratio approaches 1 ...

but in our usual case of a few dozen shots ....   it makes common sense to me that * mean radius * is much more valid .

if true how many groups do we have to shoot before group size is as valid as mean radius ?? 

********

this in preparation for standardizing analysis methods of the results of the CBA research team .

ken

 

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joeb33050 posted this 02 September 2018

hey joe ... i got one for you  >>

i believe you have explained the relationship between (among? ) maximum group size ... and mean radius ..... relative to validity ...   over a large number of shots., the validity ratio approaches 1 ...

but in our usual case of a few dozen shots ....   it makes common sense to me that * mean radius * is much more valid .

if true how many groups do we have to shoot before group size is as valid as mean radius ?? 

********

 this;  in preparation for standardizing analysis methods of the results of the CBA research team .

ken

 Group size X NUMBER = mean radius, where NUMBER varies with the number of shots in the group.

For 2-shot groups, GS X .49 = MR

For 5-shot groups, GS X .34 = MR.

"validity" = ?

We can make statements like this "Based on a buncha stuff, we're 95% sure that GS or MR = sample avg +/-  2.5%." 

There is a finite amount of information in each bullet hole. Some information extraction methods are much more difficult than others, but none that I can find increase that amount of information. A 5 lb bag holds 5 lb, whether you measure it in short tons of kilograms or cubic inches. 

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GWarden posted this 03 September 2018

I agree, but are we talking about everything being perfect, all the BS conditions? It seems that each shooter may be looking for something a bit different  in information on their groups. For some a 3 shot group supplies, other 5 shot, some of us 10 shot.

My biggest variable I run into is the person behind the rifle, me. If I am "on" and everything else has been worked to find the best load my ten shot groups the I use for evaluation can really look good. You know those times when you are in the "groove", all the planets are lined up etc, etc. BUT, give me a day where I am not on, and someone might say what is the problem with your loads or rifle, way to often the problem is me. Just my two cents worth, but I don't feel we put as much emphasis on the shooter- wish it wasn't that way.I not trying to start a hoo rah, just expressing my opinion. You all have a good day at the range.

Bob 

Iowa

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Scearcy posted this 03 September 2018

Agree. sometimes it is simply a bad day for the range as well. I shoot at a public range. Yesterday there was never an uninterrupted  stretch long enough to shoot  10 shot group. Some days I just go home and others I try to finish the group after a cease fire. It is hard to make the line safe and then return to finish a 10 shot group.

Jim

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joeb33050 posted this 03 September 2018

Today,30 2-shot = 60 shots; and 6 5-shot = 30 shots;  100 yard groups, BSA Martini 12/15, 30X STS, GECO semi-auto ~$30/brick ammo.

2-shot groups avg .604", stdev = .353".

5- shot groups avg 1.171", stdev /240".

Shooting 2-shot groups was no problem, although the groups moved around on the paper as I moved from target to target.

Then to the arithmetic  and a big surprise.

See thread "2-shot group surprise"

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Paul Pollard posted this 12 September 2018

Joe,

Where is the thread “2-shot group surprise?” I looked at the excel workbook and it looked confusing. Can we use the T Test to compare 2 sets of results? I used it on some 5 shot groups to find if one set of loads was better than another set of loads, since most of my data is for 5 shots. It cut out even looking at average group sizes. 

Do you just measure groups in the normal way, regardless of number of shots?

Thanks

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joeb33050 posted this 12 September 2018

Joe,

Where is the thread “2-shot group surprise?”

I JUST PUT IT UP.

I looked at the excel workbook and it looked confusing.

WHAT WORKBOOK?

Can we use the T Test to compare 2 sets of results? I used it on some 5 shot groups to find if one set of loads was better than another set of loads, since most of my data is for 5 shots. It cut out even looking at average group sizes.

SURE. BUT I DON'T LIKE t, t TESTS, OR STUDENT.  MY PREJUDICE.

 

Do you just measure groups in the normal way, regardless of number of shots?

YES, WITH A PLASTIC RULER GRADUATED IN TEHTHS OF AN INCH.

Thanks

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