Hi,
I really dont know what happens after a bullet hits its target (board),does it penetrate out with as much force? IF not, you can arranga another board with current conducting contacts arranged as a matrix and take all of them to some cool mC like Signal. Now, if the bullet comes out of the board with much lesser velocity then it will just strike our board (and the bullets force would not be enough to damage the board), then that particular contact of our matrix sends its signal to our mC, and all others are clear...Just a thought.

Regards,
Harsha.
PS: BTW, Congrats for your prize...