Measuring Groups

[TikkaBowHntr]

I have to test accuracy of different arrows for a school project. I am going to shoot a 3 shot group at my target, but how can i measure the groups?

[Paul L Mohr]

with a gun you normally measure the outside of the group and then subtract the diameter of one bullet hole. With arrows I normally just measure the longest distance between arrows on the outside.

Paul

[zac76156]

Get yourself a cheap 6" caliper and measure outside to outside of the widest part of the group

[JoshKeller]

Get some string, wrap it around all the arrows, and then measure the string length

[Paul L Mohr]

That would be the circumference and will be much larger than the diameter. Just measure the distance between the two farthest arrows. I just use a tape measure.

Paul

[gonzodemon]

the measure the distance from the center to center of the two arrows that are the farthest apart

[BGfisher]

What gonzo said. Center to center of the two widest shots.

[Bulzeye]

I always measure center to center too.
That way the value you end up with is not affected by the arrow diameter itself. It only mesures the difference in the points where the arrows impacted.

If 2 shooters can put their arrows's centers inside a 1 inch group, the one with the smaller diameter shafts will have the smalllest group if you measure the outside, even though both produced the same level of precision.

It's like shooting guns. A guy with a 22 could shoot poor groups, and stillhave smaller groups thana guy with a 45 that shoots better if you measure the outside. On the other hand, the 45 is more likely to score higher on a target and hit more tissue on an animal.

For actual group size, you want the center-to-center number.
The easiest way to measure it, assuming you want more than eyeball accuracy, is to combine what Zak and Paul said. Measure the outside of the group with a caliper, and then subtract one bullet diameter to calculate the center-to-center.