Specifically in Sniper Rifles, I have noticed that when I "no scope" a target (normally at close range) it appears that the damage I do is significantly less then when I'm scoping a target. This has put me in the habit of actually scoping in no matter the distance.
When I "no scope", I normally aim for the chest, being the easiest spot to hit. I decided I would actually make an effort to see if my suspicions were correct. So far it would seem that it definitely does less damage compared to scoping a target for a chest shot as they die easily in one shot, "no scoping" a chest shot usually takes 2 shots with a Black Widow on Bronze difficulty against weaker troops.
I did see the question that explained the benefits of headshots versus everything else. Which even "no scoping" a headshot will cause a death to the smaller enemies but definitely not to stronger troops that I easily one shot while scoping.
I'm hoping someone else has noticed this besides me or knows if there is something else afoot?