Moving your mouse in Insurgency Source simultaneously moved your camera as well as your hipfire aim. Sandstorm has a deadzone, so the amount of mouse movement required to turn your camera depends on where your gun is currently pointed in relation to where you want to move your camera.
This completely destroys any hope of proper muscle memory when it comes to aiming; the mouse movement required is effectively random. The mouse movement required to move your camera is the mouse movement required to pre aim before aiming down sight, because when you aim down sight it aims onto the center of the screen.
Remove the hipfire deadzone.