Your projectile always emanates from the center of you screen. While strafing with some weapon and sight combinations the sights center dynamically deviates. The amount, direction and pulsing with footsteps is different for various set ups. Also horizontal mouse input can causes more sway.
Here's another persons testing testing:
For my example I'm using the Vandal. I enjoy the NS weapons iron sights and the crack of the bullet sound. Maybe because I play allot of VS pew pew plasma sounds.
The Vandal's sway off center while strafing:
1x or 2x reflex sights = 2 red dots
Iron sights, 3.4x and 4x scopes = less than 1 red dot
1x IRNV and 6x scopes = zero deviation from center
There are other weapon and sight combos that sway in the opposite direction of strafe, making compensating confusing. For those who play TR the TRAP-M1 sway is horrendous, making a fun to use unique weapon annoying with certain sights. I seams as though the weapons that could benefit the most from accurate sights, Semi-Autos, have the worse sway.