Group Measuring

[jefats]

Greetings all,

I'm new to the forum but not shooting.

Can anyone tell me the correct method to measure a group.

Thanks
Jim

 

[Sighter]

Measure outside to outside from the furthest two shots and then subtract the bullet diameter.

For example, we shoot monthly matches that have multiple shooters competing with multiple calibers.

The shooters with 30 caliber get groups measured outside edge to outside edge -.308.

6mm shooters -.243

22 centerfire shooters -.224

This makes sense when you think about it, you are looking for the amount you deviate from the center of the bullet. Otherwise a one hole "perfect" group would measure your bullet diameter. With the above method a "perfect" group becomes a 0.0"

Hope this helps.

 

[AlNyhus]

Bullets don't make caliber-sized holes in the paper. Because of this, it's best to measure a single bullet hole in the paper and use this as the 'standard' for subtraction.

Measure the widest spread outside-to-outside (including the 'smudge' around the bullet hole), then subtract the single bullet hole measurement for the total group size. This will get you with a few thousandths of a true a group measuring device. Here's an example:

 

[RonAKA]

Agree with Al in that you need to subtract the single hole size from the outside group size. You also need to use the same technique for measuring the single hole as the group. This nulls out your measurement technique to a good extent. Here is a target shot for a fun match. The requirement is to shoot four singles, measure them all, and average them. This average is subtracted from the outside group measurement to get the true center to center group size. These are .22LR holes, and as you can see they are not 0.223", but more like 0.206".

 

[artbosco]

Can anyone tell me the correct method to measure a group.

The quick and dirty / easiest method: Take a pair of calipers, open it up to your bullet diameter, zero it out, now measure from the outside edge of the farthest two holes.