1. Change to first person view;
2. Activate free view mode (double Alt);
3. Move head to the right more than 90 degrees;
4. Press right mouse button to move into weapon sight mode.
You will notice that:
a. Your head moves back to standard postion;
b. Go to weapon sight mode;
c. Weapon moves to the right till aiming deadzone limit (didn't return to postion on step 3).