Hi!
I think what you want is a circular metal plate on which diffrent diameter circles should be drawn and the guys will attempt to shoot the inner circle with a weapon and you have to show the positon where bullet hits. And diffrent statistic about it.
I think you should use piezo-electric sensers. Actually musical instrument makers use them in drum machine to sense the hit of stick on pads. To do it i think you should cut small but thick round metalic pieces. glue a piezo speaker behind it and fit all the peices together and fill the gaps with some thing which can stand to the bullet hit. When bullet hits, it will create vibration like earth quake, i.e. strong in middle and low on outwards. So you will get respose like a very high signal at some sensor and low signal at the adjacent sensors. just monitor all of them and predict the actual place of impact.
I think same kind of idea was also stated by "Loan Nguyen" previously, but he was not to clear about it.