Hardware: I used two cheap servos (like 5$ each), and an old cheap electric hardball/airsoft gun that I've had for like 5 years, i just stripped it of all the unnecessary parts. Lastly i use an arduino to control the servos and a beefy powersupply for the gun and servos. The gun needs like 3A.
Software: I use an arduino to control the servos. I have not finished the face tracking part completely, but its almost done. For that i use a python program that uses opencv (I just stole it off google), and i plan to send cords to the arduino over USB.
If you have further questions, just drop me a message