what are some good tips on 3d tournament shooting unkown range

Practice, practice and more practice. I used to catch myself ranging different objects in my head and then stepping it off to see how close I was. I did it everywhere at work, the store, the outdoors and would do it all day long everywhere it went, before long I was getting pretty good at judging distance.

Don't second guess yourself when judging the distance what distance you first think it is, is usually right