Shangaan Hunters in Save have a nice setup similar like this:

http://www.heymusa.com/videos/HEYM_470_video_1.wmv

Main difference is that the line is a bit longer (40 m) and higher up so shooter stand under it - i.e. at the end you have to jump out of the way or the target hits you - target accelerate and you wait till it reaches 20 m, than begin to deliver - you should end up with 2 well aimed shots (from double or bolt) or compressed 3 from a bolt last one being at point blank - don't forget to jump out of the way (target is an old tyre with target fasten in the middle). If you want it more graphic you could drive a nail through the target and stuck a grapefruit on it (IMO corresponds to the brain size target). However IMO real charges are much closer - to realy test yourself you should stand beneath with your back against the target - wait till it reaches 10 m distance (you should look over your shoulder or have an apprentice to mark) - then you turn and give your best (only grapefruit hits should count).