How to measure group size

by B.B. Pelletier

I’ve covered this material before, but it was long ago, and we’ve grown in readership lately. New shooters read about group sizes and assume there’s an accurate and foolproof way of measuring them. That’s simply not the case. The great barrel maker Harry Pope once spent half an hour with a magnifying glass and a caliper to measure the size of a group; and in the end, he revised its published size by about 1/64 of an inch! So, if a world-class marksman (he held several world records) and barrel maker has trouble doing it, what hope is there for the rest of us? I’ll address that question at the end of this report. read more


How shot groups are measured

by B.B. Pelletier

Believe me — there’s enough information on this topic to fill many reports. I will do that if there’s enough interest; but if interest is confined to just one or two people, I’ll recommend that you read several of the gun books that I listed in my Building an airgun library blog.

Those books present and discuss several ways of target measurement that are considered outdated today, but which hobbyists keep trying to reinvent. One is the old string measurement in which a piece of string is stretched between the center of the target and the center of each bullet (pellet) hole. The cumulative length of the string then determines the cumulative distance of all the shots from the center point of the target. This system of measurement was popular in the late 19th century, having replaced a simpler method in which the string was stretched around pegs placed in all the bullet holes and gave the “circumference” of the group. read more