method i use is prity quick and simple,i have a ball of string which has a knot tide every 5 mtrs ranging from 5 to 50 mtrs ,i also draw a picture of the reticle on a peice of card,lay the string out and then zero gun at point that suits, lets just say 25mtrs ,then move the target to each knot i have tied a make a referance to the drawing ,once i done that i stick a peice of card in the back of my flip up lense cap
here's acouple of pics to help explain