If you find yourself shooting and not killing, you probably need to lower your sensitivity. Keep lowering it untill you can't play with it any lower than practice with that. Also, don't spray. Unless their in knifing distance, you shouldn't be spraying. Take your time and stay calm once confronting and enemie. They will probably be spraying you and not hitting you. If you keep your calm and burst your shots or single fire, you will get greater results.

Peace,

Valor.