Mate,
I was doing what you seem to be doing, at the begining of the year. Just get a 40 Yard/Meter(Whatever's your preference)ball of string and tie a twig in it every 5 meters, from about 10 meters on.
Stretch it out on the ground and dig an old spoon in to the ground by it's handle, next to each twig. Having checked your zero, first of all shoot the spoon at your zero, then work up and down the line.
It might take you a day, and seem really boring to think about doing, but when you can happily shoot up and down the line in no particular order, hitting each spoon head, you've cr