Group measuring. OK guys

[TAJ45]

A long way from a salty expert here but out and out subtraction of the cal dia from your outside to outside msmnt isn't accurate.

Some .22 rimfire disciplines/orgs require a bullet of the mfr used to shoot the group, be shot well off to one side and labeled as such to be measured for the actual result after punching the paper.

We usually have calipers, so do the one hole measurement on several holes, be honest with yourself, average and subtract that from the group's size.

I haven't had the cals out for a group in a while and forget what redux I need as an average for the different cals. Of course, when we start getting kinda serious, we find that paper composition and day's humidity will be factors. As a toolmaker, I am of the opinion that if I post in thousandths, then I need to do "thousandths" due diligence with my measurement - basically an average taken on separated shots. I don't factor humidity, thickness of backer yada yada & etc.

I personally knock off .020 - .025 and ym certainly mv.

All this said with a big

This is NOT an attack nor is my nose out of joint that someone's claim needs to be reduced .021" - just a bit of background facts of this hobby.

 

[jimcasey01]

Weight and composition of the target paper will definitely make a difference. Using a .223 (bullet diameter .224) I have found .2 is a more accurate number to use. From the best I can tell, my holes are typically .200-.205 diameter on 110 lb card stock.

 

[pacificman]

I have just recently learned about measuring outside to outside of group then subtract caliber...to me it seems like cheating or bragging... : ;D. But it is probably designed to give a more accurate account of group sizing and sounds like the way it has always been done. To me it sounds like it would be mandatory for the competition shooters as it could be a thousands of an inch to win or lose. I can see your point about target paper etc. being a factor in all of this. While I don't compete in any bench rest shooting I'm glad to be able to have a comparison or example to go by as this is where I can learn more info. Good post man.

 

[BoydAllen]

In CF short range group competition, a caliper attachment, like the one that Neil Jones sells is used.
http://www.neiljones.com/html/target_measuring.html
It is more accurate than using a caliper alone. In any case, measuring, or centering a single bullet hole shot through the same paper and backer should be part of the process.