Measuring Groups
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I think I have an idea how to do it and I don't have a new fangled downrange camera set up so lets see if I am a complete idiot when I get my yardstick out to measure my groups. Lets say I shot three shots at a target holding center of the bullseye for every shot and they make three holes. I wish I had some graphics. Okay, they're all around one another so I get my caliper or whatever to measure it. This is how I do it so correct me if I'm wrong. I measure the widest points outside to outside of the three holes. Now at this point I can do a couple of things. I can record that measurement and subtract one diameter of the projectile I am shooting or position the caliper or ruler on the outside edges of the two widest holes or eyeball for center and say that's not too bad and record it. I know paper gets torn up and sometimes the back of the target blows back through so without the optical thing it can be off a smidgen. When I worked in the machine shop that's how I measured centers on holes of parts we reproduced by measuring outside of two holes with pins inserted in them or screws then subtract one diameter of the pin or screw. The eyeballing never works. That's all fine and dandy for clover leaf groups. There is some people that can shoot groups that are one single hole. I have no experience in this maybe one day I will. So the big question is how do we measure that? Here's my theory, lets say the one hole group you just shot (five shots) has a diameter of .500. You shot it with a .22 rim fire so what do you do subtract .224 from .500 and that makes it a .276 group? I'm not trying to be a smart ass just never had the problem of documenting a one hole group. I remember going to the carnival and trying to shoot that dang red star out with the crappy machine guns they had and there was always a tiny red sliver left. :(
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Yes, you measure outside to outside and subtract bullet diameter. For 22lr, it’s .222.
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I shot a bit today with a tuner, so I figured it was a good opportunity to give you a little guide on how I do it. ;)
Dial a digital caliper to the bullet diameter. Then zero it out.
Next, measure as precisely as possible to the outside of the group. Look for the outermost bullet contact, rather than the paper tear. Paper tears can be deceiving. Since you already zeroed out the bullet diameter, the number you see on the caliper is the group size.
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@orkan Didn't think about digital calipers usually I keep a cheap dial caliper on the work bench. You're having some fun with that rig and it's just the beginning.
