How to measure a group?

[Three-Fifty-Seven]

I was out shooting my 22 this morning, and for me I did quite good I think, but I want to confirm the proper way to measure a group . . . besides we have a postal shoot which ends next weekend, and I need to know who wins!

Here is my best target I shot this morning ten shots from the roof of my car at 50 yards:
http://i153.photobucket.com/albums/s220/ShawnTVT/Guns/Measuringgroup.jpg

Now somewhere in the back of my brain I think I'm supposed to measure it the way I did, then subtract diameter of one boolit. (which would give me a center to center distance)

Is this right?

If so . . . then I shot all ten inside of 0.854" (1.074 - .22 = 0.854)

With round pointed ammo, I do realize it is hard to get to the "edge" of the hole, how close do you go, should I have gone till no paper is showing?

[1Shirt]

Thats one way to do it, OR----you can measure from the inside of the farthest shot to the outside of the farthest on the opposite side. Just about the same thing. Neither is exact depending on the measuring technique of the guy doing the measuring, but is close enough probably for Govt. work
1Shirt!:coffee:

[c3d4b2]

Here is a link to some software that helps to measure. You need to use the scale reference for pictures.

http://www.ontargetshooting.com/index.html

[Houndog]

Outside to outside minus one bullet diameter is how they do it in Benchrest.

[lwknight]

The edges are iffany at best. You just have to use your own unbiased judgement on that part.

[crabo]

I try to do center to center, that works best for me visually.

[geargnasher]

Use meausuring plugs on the farthest holes, make sure they are perpendicular to the paper, mic the outside-to-outside and sub one boolit diameter. Not THE way, just A way.

Gear

[Doc Highwall]

You are doing it correct. This is what I use making it easier to determine the edge of the bullet hole. This set is available from Sinclair International and is made for 22 Cal, 6mm Cal and 30 Cal.

[geargnasher]

Now that's slick, Doc.

Gear

[Echo]

One thing I learned in Grad school is that one introduces error when one measures something. Whatever it is, IT IS. Since that is the case, as long as one is consistant with their methodology, the actual value isn't as important as the relationship that value has with other values measured with the same methodology. So one is 10 thousandths off - so? Works for competition, too.

[mike in co]

Thats one way to do it, OR----you can measure from the inside of the farthest shot to the outside of the farthest on the opposite side. Just about the same thing. Neither is exact depending on the measuring technique of the guy doing the measuring, but is close enough probably for Govt. work
1Shirt!:coffee:

but hard to do with calipers...when the caliper covers the hole, when are you at the edge ?

[mike in co]

One thing I learned in Grad school is that one introduces error when one measures something. Whatever it is, IT IS. Since that is the case, as long as one is consistant with their methodology, the actual value isn't as important as the relationship that value has with other values measured with the same methodology. So one is 10 thousandths off - so? Works for competition, too.

actually if you check with br shooters you will see when targets are measured by multilple people with measure experience...they are very close....no 0.010 ...closer to .001....

the tool shown above works. as does the visual/optic centering tool that is then moved to the other hole and the difference is the group size.( the centering see thru pc is placed over a hole, and centered. a holding pin is push and the calipers expanded from the pin till the optical tool is centered over the second hole, the meassurement is a direct read out of group size)


several tools on the market for this, some require a caliper added.

another requirement is good target paper, a good backer so that crisp holes are produced.
yes you did it the right way....

mike in co

[HeavyMetal]

I guess it depends on what your doing when you measure group size, as does how many rounds are fired into a specific group.

While I realize many forms of shooting, such as "Benchrest" competation, use the center to center group size measurement I have never been comfortable with making the kind of claims I've seen or heard of.

I also realize ths is sort of blasphemy but I simply use five shot groups, and measure edge to edge because my thought is this is the real group size! For my personnel shooting this is what I do.

I am not being critical just my observation so the group pictured would be 1.074 in my book and veery nice indeed for 10 rounds fired from a production 22 rifle at 50 yards!

NIce group Shawn.

[Doc Highwall]

The reason you subtract one bullet diameter is because you want to measure center to center and not outside to outside otherwise the person with a larger caliber gets penalized just because his caliber has a larger diameter.

[Three-Fifty-Seven]

This is just for a friendly postal match, nothing high dollar, just bragging rights! Check my linky at the bottom, and join up!

We are shooting ten round groups to give a better picture of true accuracy, instead of the lucky three shots . . .

Yes the gun is just an old Rem 513P only mod is I pulled the peep and drilled and tapped for a scope, which I put on a Nikon Buckmaster 3X9 I pulled of my 270 . . . I think I can do better but shooting off a towel on the roof of a car . . .
http://i153.photobucket.com/albums/s220/ShawnTVT/Guns/Remington%20511P/Rem511P22.jpg

[imashooter2]

I always go inside edge to outside edge of the farthest spread. I call the edge the end of the radial tears. You can tell if there is a tear that is significantly longer than the others. Discount those. In your picture, the caliper is about right on the upper hole, but well inside the bullet diameter on the lower.

Scoring plugs are best as they take away a lot of subjectivity, but few folk actually have them.