Need help with LookAt - Object flipping

Hi there,

I have a gun that I need to rotate around the Z axis and follow the mouse. I have tried so many different methods and they all work, apart from one thing. When the mouse crosses the Y axis above or below the gun, the 3D gun model flips 180 degrees on the Y to keep facing the target. I need it to rotate without flipping. It only does this when it crosses the Y axis.

I am not to good with this mathy type stuff... any ideas why this would be happening? As I said, I had many attempts and the most basic (LookAt) is probably the best way to go... I also tried Quaternion.LookRotation... same issue (I had thought it might be gimbal lock).

Any ideas?