Practice, practice, practice! I know the same exact feeling your experiencing. I always considered myself a good shot in my back yard. For hunting situations I too always knew my lane distances, and often even placed a small ribbon at my max yards. My first 3d course I was terrible. What a wake up call!! I know enjoy it so much, and have increased my shooting ability 10 fold. Here' s what I did for 3d practice. 1st I bought a 3d target. Next I made up some cards with variety of distances on each. From 10 to 50. I' d mix them up, and either myself or kid would pull a card. Walk out in front to the target where I thought that distance was, and shoot it. I' d do this at least every other day for 20 to 30 shots, and score myself. Once I felt I could pick out distances decent. I had my kid place any ol' target for shooting, anyplace in yard without looking. He' d say ok dad. I' d turn around judge it, and shoot. To continue this on none shooting days. While taking a simple walk in the woods. I' d pick out a tree, stump, critter, whatever. Guess the distance. After a month of practice I was alot better, and even better today. I never once used a range finder, as I felt I' d become to reliant on that, but thats just my thoughts. I hope this helps, or gives you some ideas of my own.