Dont most skybusters use a range finder so they know the birds are within there effective range? 
Rangefinder

I have gone to these places this is all about with a arc rangefinder. Stood close to the action. and shot ranges. WOW is all I can say

A good way to figure distance is. walk around with a rangefinder. Make a guess at a distance. then confirm it with the rangefinder.
With a shotgun 5 yrds isn't a big deal until your at the end of the killing range. And because a shotgun will shoot xxxxx distance. Doesn't mean that is the killing range. Ya ok you hit one in the eye you might kill it.