Yes, Chairgun is an excellent start point but, in my opinion, you then need a bit of range time to fine tune the dots ... or parts of dots. Open air is good if you have a no-wind day but even a slight breeze can produce horizontal and vertical movement depending on the location / terrain. But again, you will get good indications. I know people who visit indoor ranges e.g Pete's Airgun Farm (?) just for this type of facility.
Cheers, Phil