How do you measure the shot group
When you buy the best air rifle you expect it to be extremely accurate. However, there are different definitions of accuracy. A person may consider his as the best air rifle as he is able to shoot a can which is 20 feet away. The other may only consider his gun accurate when he can hit a bird’s eye when he or she is 50 yards away. Accuracy therefore is a very subjective term.
In order to understand accuracy, you need to understand a shot group. This is one of the ways to check the accuracy of the gun and that too not subjectively but by using math. This is how the shots are arranged in the group when the gun that shoots just one projectile in a shot. The shot group size is the distance between the center portion of shots which are farthest apart. This is also called as c-t-c or center-to-center.
The group is measured by the distance being measured by the far edges of the shots that are the widest and having the diameter of the bullet subtracted for it. This will give the distance between the center of the shots. If the widest shots in a group of shots which were fired by a .22 caliber rifle measures 1.22” when the width across the widest distance is taken then the c-t-c is 1”. This formula works on all groups as well as on all calibers.
However what you need to remember when you are measuring the group spread is that the bullets will tear through the paper raggedly and so the actual true edge needs to be found. For starters, the pellet can be inserted for ease till one gets used to calculation of it.
The group size can be measured by ordinary rulers or for more precise measurements, calipers can be used.