In ideal conditions I've watched dogs come to a spitfire/wildfire from around a half mile. That seems to be a pretty universal rule of thumb for the way I call, no matter what calls or caller I'm using, but some callers are louder than others. Maybe i should say it's more about how far a dog is willing to travel? which obviously varies depending on the dog and the day. Running a caller full blast can backfire on you sometimes too, so ease into and out of it.