I always wanted to shoot things in virtual reality but I'm broke so I did what I could. This is my attempt at an Oculus Rift style experience with Google Cardboard. This is actually a really fun project and its extremely easy to replicate. The parts cost around $15 total and will take about 45 minutes if you are new to Arduino. It utilizes the smartphone that you already have, the only caveat being it must be compatible with google cardboard. The game was made in Unity 3D with the Vuforia augmented reality plugin. You do need a virtual reality headset which can be had for around $15 as well. This is the one I use: http://amzn.to/296KwbJ

The Android App and iPhone xCode project can be downloaded here as well as the Arduino code (there is also a list of parts with links to exactly everything I used): http://www.wirebeings.com/virtual-reality-gun.html