Say a player has 120 HP as an example
(All 100% acc)

Player gets all body shots: 120/18=6.6666=7 hits to kill.
0+7
7/5=points

Player gets all headshots (40 on first because of helmet, then 50)
120-40 on first shot, 80/50=1.6=2 shots
3 shots total
3+3
6/5 points

7/5 points for 0%hs
6/5 points for 100% hs