The external ballistic (the white-greyish line created from the bullet) is slightly moving from the right top corner.Meaning someone else was shot by that guy giving you a window of ..let me think.. about 2-3 sec to reaim at you and to fire? At that time the possibility of you hitting him is different. There is a possibility of him moving giving you a total fail, there is another possibility of him killing you first and there is the other possibility of you damaging him but not killing him and also the one of killing him. That gives you a 25% possibility of killing him,witch will happen only if he had shield down because hitting someone at that spot wont kill him but will reduce is health a lot(its a 50/50 chance based on the health) Final result? 12.5% possibility of killing him.It all depends on the 2-3 sec given to you to take action. But supposing that the guy had full health, you failed. Well i might also be wrong