I have recognized several weapons sound slightly different when they are aimed down the sights, and i believe that this is a intended soundeffect.
But on the Pistol for FOPS/Engineer these soundchanges when using Ironsights are tremendous, much bigger than on the other weapons.
They change from (how the **** can i describe sounds?) a dark and heavy “boom” to a light and sharp “tick”.
I don´t think this was intended.