It actually doesn't require a normal distribution. If special causes like barrel rubs and shooter flinch have been eliminated, so that variation is random, then it will give about the same answer as calculating SD by its definition, the sum of squares. If special cause is present, then the classic sum of squares route will give a higher number.
Standard deviation is a measure of variation.
Range is a measure of variation.
They are different measures of the same thing, and can be converted back and forth. If the subgroups have few items, the conversion is pretty good.
If you are shooting five shots, range is about as good a number as you can get.
