How to measure groupings

B

BuckRub

Moderator
I've heard this several different was but do you say measure overall fartherest rounds. Say your grouping consisted of 10 rounds. Get the two fartherest ones length overall and subtract a bullets diameter.
 
You got it.

You can also take your calipers, measure a bullet, zero your calipers, and then measure the group. By zeroing your calipers, it'll subtract the bullets diameter automatically and they'll be no math involved.
 
I'm really surprised that someone hasn't made an app for IOS or Android to do this. It should be pretty simple. (I know it doesn't answer your question directly)
 
Yes, center to center is the appropriate approach or measure edge to edge and substract a bullet diameter (actually the diameter of a hole in the target). I generally just use edge to edge for my personal group measurements, but I always state such if I make a statement about my groups. I use a digital caliper.
 
For quick and dirty you can measure from the outside edge of one hole to the inside edge of the other hole and be pretty close. Not the best way but good enough for government work.
 
The easiest way is to find the 2 holes farthest apart. Measure from the inside edge of one to the outside edge of the other. This way you don't need to subtract bullet diameter and is more accurate than trying to "eyeball" the center of the hole.
 
There is also a PC application called On Target that will do this from an image of the target for you. There is a freeware version and a paid version with more features.

The only trick using this program is to have something in the image that you know the length of, like a grid or a line you make with a ruler in the image. A scan of the target is best, as it doesn't distort, but camera photo's work. Just make camera photos as square to the target as you can using as much telephoto as you can to keep the image flat and undistorted at the corners. When you have that known length in the image, you click the ruler function, then click and drag the mouse from one end of that known length to the other. This scales everything else.
 
Last edited:
For practical purposes, posts 6, 7 and 8 are fine and the method I always use. For competition, especially bench rest, a more precise method is appropriate (necessary?).
 
Same here. I feel like the author gave so much away with that free version that there's no point in upgrading. I may do it anyway, just to support his efforts, but that freeware version works fine.
 
Yep. Measuring. That's where On Target helps. By placing the bullet hole circles over the the actual fired target image, you can often spot the bullet soot smudge edges on the paper and locate the circles very precisely. The human eye is good at the kind of averaging needed to do that.

One Apple I-phone application appears to work the same way, using the phone camera to image the target, plus it scores the target if it is in its database.


Wogpotter,

Did you check with PointBlank that it was OK to post their copyrighted image format? See the board policy on posting copyrighted material. Data itself (raw numbers) cannot be copyrighted, but a particular graphical representation format for it is automatically copyrighted under current copyright law.
 
Last edited:
Not wanting to cause problems I removed it.
I honestly think they'd probably not complain about free publicity, but its gone, sorry.
 
wogspotter, you'll get no argument from us about such things being silly but that is the current state of copyright law and lawsuits.

One would think that free publicity is always good but the companies do have the right to control their images and forums can be and have been sued to remove them.

There is no problem whatsoever in including a link to their page and discussing their product, you just can't use their images without permission.
 
Measuring pistol groups:

Measure greatest distance between two holes. Divide by 2 until you get < 3" group.

Measuring rifle groups:

Measure greatest distance between two holes. Divide by 2 until you get MOA.
 
You must log in or register to reply here.
Back
Top