Video Guide:
In total there are 9 different shots we can make; however, we only need to do 8 of them for the achievement across our entire time in the game.
Those shots are:
Headshot (Brain)
Eye
Lung
Heart
Liver
Stomach
Intestines
Kidney
Testicle
The video above shows all of the possible shots in the Shooting Range for demonstration purposes, the achievement can't be completed in the Shooting Range. Instead, in a mission knock an enemy unconscious with melee. Pick up and position their body flat, then create a manual save. Now, use the rifle to hit each of the organs, reloading the save after each shot.