The touch-object can get the angles of the device, you can use these to make your bullet move..
From the manual:
Compare the current device's motion as its acceleration on each axis in m/s^2 (meters per second per second). The effect of gravity can be included or excluded, but note that some devices only support accelerometer values including the effect of gravity and will always return 0 for acceleration excluding gravity.
Compare the device's current orientation, if the device has a supported inclinometer. Alpha is the compass direction in degrees. Beta is the device front-to-back tilt in degrees (i.e. tilting forwards away from you if holding in front of you). A positive value indicates front tilt and a negative value indicates back tilt. Gamma is the device left-to-right tilt in degrees (i.e. twisting if holding in front of you). A positive value indicates right tilt and a negative value indicates left tilt.