Ring around bullet caused by seater die

[FlyFish]

Group size is defined as the distance between the centers of the two farthest apart shots in the group. As a practical matter, it's easier and more accurate to measure the distance between the outside edges of the two holes, then subtract one bullet diameter.

 

[briandg]

The reasoning behind that is that the center of the hole is the actual point of impact.Outside border doesn't define impact, but as he said, just cut caliber out of the total distance from edge to edge.

when you reach the point of groups the size of a tennis ball, unless you are really feeling the need to, just count it from edge to edge.