Mesuring Group size - comparing three methods

[fljp2002]

Fellows

Was out yesterday and for fun decided to compare methods to measure my group sizes.

Method 1 - SubMoa App. How it works: Take photo of target. Using know distance on the photo (I placed a steel ruler beside the group) indicate the know distance to the app. Indicate bullet on target and the app calculates your group:

Method 2 - Drawing Circle template. How it works: Place template over group. Using found measurement, deduct 5.63mm (I measured a unfired bullet (last photo) to get centre to centre point. In this case my group fit in the 23.812mm circle minus 5.63mm = 18.29 mm group.

Method 3: Digital Micrometer. How it works: Measure group with instrument. Using found measurement, deduct 5.63mm (I measured a unfired bullet (last photo) to get centre to centre point. In this case my group measured 24mm minus 5.63mm = 18.37 mm group.

In summary, the app allows you to have nice graphic and quick calculation on the range but is the least accurate. The circle template is easiest but if you group is between 1/16 to 1/8 inch you may not get a fully accurate reading. The Micrometer is very accurate but you have to be careful when measuring to get the exact edge.

Best bang for the buck - Steadtler Professional Combo Circle. Its also the easiest to use.

 

[Hardhammer]

Thanks, very interesting post and love the Staedtler circle method.

 

[GUB]

I like the circle method..Used it before and great visual reference with the circle lines on the target

 

[Mystic Precision]

Thanks for the test... very good info.

I will stay with the manual method...

Jerry

 

[RabidM4U5]

One flaw with your manual measuring methods, you are subtracting the diameter of an unfired bullet. Bore sizes vary, but they all squeeze down the bullet diameter, and the holes in the paper are thus smaller than the unfired bullet. The holes in the paper are usually around 0.215" or 5.46mm. Measure several and take the average. Your caliper appears to not be quite aligned with the edge of the top-right hole, the group is a couple mm larger than you think The app is very precise, the human hand, not so much.

A couple comparisons of app vs manual measurement. This was On Target software, not the same app you used. First was someone else's target they posted and I downloaded to check their measurement.



Then mine that I measured manually first, then checked with the app

 

[grauhanen]

Rabid makes a very important point. The bullet hole in the paper is smaller than .22". Furthermore thin paper like that used in photocopying tear easily and don't leave a neat hole. Target paper leaves the cleanest holes, but it is not typically available at places that photocopy targets (printing them at home is too expensive). Card stock, 65lb weight, is good for copied targets and it yields a reasonable hole to measure.

It's also important to measure the gray "smudge" left by the lead bullet as it passes through the paper.




Note: A figure like .215 or .216 should be used as the bullet size to deduct from the edge-to-edge (including the gray smudges) measurements made with calipers. The range where I regularly shoot has it's 50 yard targets actually set at a measured 57.4 yards (172' 4") from the target to the outer wall of the shooting building. Since my shooting distance is over 50 yards I deduct .22" from the outside-edge-to-outside-edge caliper measurement.

I would like to think that a target app like On Target is the preferred method of measuring. It should be very accurate. But despite having it on my laptop I have to admit that my level of competence with its technology has prevented me from understanding how to make it work.

 

[fljp2002]

Looking through the my rifle shoots 1/2 inch And under all day Thread , most if not everyone is using .221 as their deduction.

Rabid makes a very important point. The bullet hole in the paper is smaller than .22". Furthermore thin paper like that used in photocopying tear easily and don't leave a neat hole. Target paper leaves the cleanest holes, but it is not typically available at places that photocopy targets (printing them at home is too expensive). Card stock, 65lb weight, is good for copied targets and it yields a reasonable hole to measure.

It's also important to measure the gray "smudge" left by the lead bullet as it passes through the paper.




Note: A figure like .215 or .216 should be used as the bullet size to deduct from the edge-to-edge (including the gray smudges) measurements made with calipers. The range where I regularly shoot has it's 50 yard targets actually set at a measured 57.4 yards (172' 4") from the target to the outer wall of the shooting building. Since my shooting distance is over 50 yards I deduct .22" from the outside-edge-to-outside-edge caliper measurement.

I would like to think that a target app like On Target is the preferred method of measuring. It should be very accurate. But despite having it on my laptop I have to admit that my level of competence with its technology has prevented me from understanding how to make it work.

 

[Longstud]

Rabid makes a very important point. The bullet hole in the paper is smaller than .22". Furthermore thin paper like that used in photocopying tear easily and don't leave a neat hole. Target paper leaves the cleanest holes, but it is not typically available at places that photocopy targets (printing them at home is too expensive). Card stock, 65lb weight, is good for copied targets and it yields a reasonable hole to measure.

It's also important to measure the gray "smudge" left by the lead bullet as it passes through the paper.




Note: A figure like .215 or .216 should be used as the bullet size to deduct from the edge-to-edge (including the gray smudges) measurements made with calipers. The range where I regularly shoot has it's 50 yard targets actually set at a measured 57.4 yards (172' 4") from the target to the outer wall of the shooting building. Since my shooting distance is over 50 yards I deduct .22" from the outside-edge-to-outside-edge caliper measurement.

I would like to think that a target app like On Target is the preferred method of measuring. It should be very accurate. But despite having it on my laptop I have to admit that my level of competence with its technology has prevented me from understanding how to make it work.

Just out of curiosity. The targets shown in ur post have "Rimfire Junior Practice 500 meters". With a rimfire and a junior shooter, that's quite a difficult target Id think. Maybe start them on something a little more attainable to prevent frustration. Or you could load them up with a special batch of that ELEY ammo we all know you have. Cheers Chris

 

[RabidM4U5]

Looking through the my rifle shoots 1/2 inch And under all day Thread , most if not everyone is using .221 as their deduction.

Yes, while permissible as per the challenge rules, this action does not generate accurate measurements. I'm fine with grauhanen using the handicap, as someone must have had a few too many Bud Lights while measuring out the berm distance at his range. Truthfully, it is such a minor difference that we're just splitting hairs, none of our targets are up for Guinness world records after all, but if you want to be fully honest with yourself... you know what to do.

 

[Mystic Precision]

Just out of curiosity. The targets shown in ur post have "Rimfire Junior Practice 500 meters". With a rimfire and a junior shooter, that's quite a difficult target Id think. Maybe start them on something a little more attainable to prevent frustration. Or you could load them up with a special batch of that ELEY ammo we all know you have. Cheers Chris

Me thinks a typo



490m for me yesterday.



Kids Hoola Hop 19" ID... with the gusty winds, let's just say, group size was generous



But we did put hits into and on the ring... I don't think I am going to need to worry about bullet diameter with this type of shooting.

Tons of fun .... for like $15 worth of ammo. Best value in LR shooting I know of.

Jerry

 

[horseman2]

This is a Rimfire Central target. The four targets down the middle required one shot per target.
Each bulet hole was measured and the average of the four became the amount to be subtracted.
IIRC there were a number of measurements below 0.20.

 

[Buck1950]

Some measurements . . .

Hi - This chart shows measurements I made last fall after I slugged both of my 22s. Granted, I just used a $15 CanTire caliper, but they're pretty close. I was comparing the measurements of various brands of cartridge to the slug sizing I found to gauge which ammo should be most accurate. I didn't find a significant correlation, but I've only used a few groups of 5s to check. Too many things going on last Fall to pursue this, but Summer is here. I've been stocking up on 22 ammo
At the bottom are the sizes of the slugs I ran - only 3 slugs per rifle, very tedious
Those numbers suggest that I should be using 0.224 for the holes I've always used 0.221 as many others above . BTW, I measure at the outside of the 'smears' since the paper bends a bit ;-)

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