Settings alone won't guarantee headshots; these techniques are critical for CS 1.6's engine: Crosshair Placement
cl_dynamiccrosshair "0" crosshair "1" crosshairsize "2.5" crosshairthickness "0.5" crosshaircolor "5" // Green or Red for contrast cl_crosshair_color "0 255 0" Cs 1.6 Cfg Aim Headshot