There is a very small window (so to speak) on the human body that will give a one shot kill.
A short T, eyes down the nose to the upper lip, that's if the target is facing you, the target alters as the body rotates. Then you have a vertical target at two inches wide (spinal column ) and this can be easy or hard to hit depending on how much penetration is needed to reach the target, is it facing you, angled to you or are you shooting from the rear ( the nasty back shot).
These are extreamly small targets to hit at the best of times and they get smaller as the pressure goes up.
Military experience is just what it sounds like, but that does not equate to combat experience. Shooting under pressure and hitting the target is what counts.