I was pointing the camping rifle at a bot's head unzoomed.
Every time I shot the primary fire, I heard a damage indicator and a voice saying "Headshot".
When I zoomed in on the exact same spot on his head from the exact same distance and angle and shot the primary fire, there was no damage indicator or headshot voice.
It appears the bullet behaves differently when it is fired with the player using zoom than without the player using zoom.
I don't know if that's a bug or not, so I posted here.