damage handicap?

Does anyone know if there is a damage/shield handicap in multiplayer? Recently it’s taken well more than a normal amount of head shots to kill an opponent. I just finished a game where I emptied a full DMR clip into an opponent, half to three quarters of those were head shots and he did not die. That is the most egregious one but similar things have been happening regularly. My K/D has gone from 1.6 to 1.2 in about two weeks.