Godo for you and luck to you.......and you are doing the right thing - knowing where you gun shoots and knowing your maximum range is a big plus!

Now once you have your Maximum range - learn distances. If I have time (sometimes you need to sit n a hurry) - I'd place a stick out 20 paces sticking up out of the ground as a reference. Now I use a range finder and range certain visual aspects such as an ant mound or a certain tree or bush - so I know. Helps me as I use those as a goal to get the bird too.

Have fun and pay attention - I am taught a lesson or two each yr.
JW