Excuse me, mother ****er?Try hitting the head.
You don't even need to be sharpshooter.
I reached level 3 Sharpshooter without even playing the perk. I ALWAYS aim for the head, so stop assuming ****.
I just reread your post; apparently I misread it previously. I thought you had said you get 1-shot-kills when hitting the head on Scrakes, with a 9mm.
Oops... my bad! I apologize good sir.
[P.S. - I kill all those you listed with 1 bullet to the head from a 9mm as well. I must of been on too many opiates when I read your post or something... ]