If you like shooting, then you need proper and not monotonic target system. Shooting cans may become boring and too engaging when you need to set things up before practicing. Bob decided to make things more easier with Atmega168 based target rig, where he placed several servo motors on 3D printed structure covered by steel angle for protecting sensitive parts.
Arduino on target structure is equipped with Xbee for remote control. It can work in several different modes like single target, dual target mode with random patterns. From there you can thing of many ways what targets you attach to servo motors – color circles, faces, that vary in size and so on.