Just thought I would throw this out as I have run up against so many ways to decifer a grouping. This is a real group an dnot a trick question or anything. Just want to know how others would call it.
A three shot group in a triangle shape. Two at the bottom in line and one at the top. Starting from the left we will name the holes A-B and C at the top. Distance between the center of A and B is .500 (1/2 inch) The distance between the center of C-A is .500 also. The distance between A-C is .650. So what is this group?

It is so a trick question. What is the distance between C and B and how can you have two different dstances between A and C??

Groups are commonly measured by taking the extreme outside spread of all shots,then deduct the diameter (example .277).This will give the true center to center group size.

No not a trick question at all. I got my measurments off. Let me correct and then go with it.
A to B .500

C to B .500

C to A .650
Ok now what do we have?

Ok bowhunter the extreme outside from where? I am serious about this. From the outside of A to the outside of C equals .625 + .264, since .625 is from center to center. So .625 + 264 = .889. Subtracting .264 from this it leaves .625. Is that right?

It's a .625 group.
You can also have 4 rounds through the same hole and one off to the side and get the same answer as your looking at "extreme spread", not "group after throwing away the ones you don't like".

quote:

Originally posted by Tailgunner:
It's a .625 group.
You can also have 4 rounds through the same hole and one off to the side and get the same answer as your looking at "extreme spread", not "group after throwing away the ones you don't like".

Ditto!

Blob
As you changed numbers on me between posts (.650 and .625) I went with the number given in your last post (.625). If the origional number (.650) is the correct measurment, than that's the one. Sorry about any confusion.

Hey tailgunner numbers is one of my down falls as the old head gets older! I mean a simple 1 + 1 comes out 5 sometimes! I see I have been measuring my groups wrong. I figured this was a .625 group but I have been using circles and things that don't add up. Like I say the old age is creeping up! Thanks for all the help.

Normally we measure groups as the distance between centers of the farthermost two holes. In cases of almost equilateral triangles like this I use a circle template to find the smallest circl;e that contains the centers of the three holes.

Jusat guessing the actual group size is around 3/4".

Put it on cad really quick. .658" center to center.

I combine a group size analysis method (extreme spread) w/ an error analysis method (vertical and horizontal spread). This was taught to me at Quantico and I've kept the practice. There are several group and error methods practiced.

Gary

Boy I must be a simpleton. I thought a miss was a miss, a group was measured centre to centre of the furthermost shots apart.
I also thought a group is not worth two bob if it's not centered.

Jees we have a character here in the Nat Rifle
Assn. who when discussing groups, ends up using only graphs. Don't know if anyone knows what he's on about.
JL.

Only shot one time from now on and you don't have to worry about such non-sense. You will only have one hole and you can lie to your buddies like I do and tell them its a 10 shot group.

quote:

Originally posted by Blob1:
Hey tailgunner numbers is one of my down falls as the old head gets older! I mean a simple 1 + 1 comes out 5 sometimes! I see I have been measuring my groups wrong. I figured this was a .625 group but I have been using circles and things that don't add up. Like I say the old age is creeping up! Thanks for all the help.

Not really 1 + 1 = 3

If you don't believe me ask a pregnant woman.


Measure Outside to Outside and subtract one bullet hole size, or measure Inside to Inside and add one bullet size, or measure Inside to Outside and subtract no bullet size. There are two many ways to get the same answer.

Also if I am not incorrect you need to consider when measuring holes that not any one of the holes actually measures the same size of the bullet, so the extra missing size of the bullet needs to be added.

Confusing ain't it.

Yep but they all have only one centre and us peep shooters know how to find it. :-)
JL.