How do you measure the size of a group?

T

thumbtack

New member
I need clarification. What is the standard way to measure the size of a group?
If there are two shots (I am using two just to make it easier.) Let say that Hole A is on the left side of the target and Hole B is on the right. Do you:
1) Measure from the center of Hole A to the center of Hole B.
2) Or do you measure from the outermost edge of the Hole A to the outer most edge of Hole B.

I have always measured from the outermost edge to the other outermost edge. Is this right or am I way off.
 
Method 1 (center to center) is the correct measurement.

Consider this: if groups were measured from outside edge to outside edge, then it would be impossible to shoot a group smaller than the bullet's diameter, even if you put all your rounds through the same hole. This method would also make larger calibers seem less accurate than smaller calibers.
 
Thumbtack, group size is measured center to center. But I believe the most common way to do this is measure the distance between the two farthest edges and subtract one diameter (caliber).
 
If you ask enough questions...

If you keep asking questions, maybe you can reduce your group size to "zero" hehehe
 
Center-to-Center, But- - -

Leigonnaire has it right, but a simpler, easier way to measure ctr to ctr is:

Measure from right-side edge of rightmost hole to right-side edge of leftmost. (Or top edge to top edge, etc.)

This way, you are automatically deducting one bullet hole diameter which equates to a center-to-center measurement, without worrying about finding center of the respective holes, or the subtraction operation, which presumes you have the correct bullet diamerer.

And, instead of using a ruler, if you measure with the same dial calipers with which you measure case length or C.O.L. in your ammo, you have the measurements already in tenth, hundredths or thousandths.

Simple, huh? Our own forum member Stephen Camp showed me this trick just a few years back, after I'd been doing it the hard way for decades!

Best,
Johnny
 
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