I've ran up a few times to non playing enemies and used the shotgun point blank to their head and no kill. I've used the SCAR 1/2 magazine into an enemy's head while they take the genius thought of running straight but STILL no kill.

This is a serious question... Do headshots EVEN count?

Umm are non playing enemies the AI or online game?

Umm are non playing enemies the AI or online game?

Online multiplayer. And ACTUAL players that are away and have their character standing completely still.

I never encounter idle people... But recently I've been spawned right next to an enemy player.... It didn't end well for them..

It's because of the nutsoid server lag and the bizarre bullet system, insane. Aim for the upper chest, you'll get a lot more "headshots".
Don't aim for the head, you'll just miss with half(or more!) your bullets despite your screen showing hit confirms.

<3 people who think the hit confirmation is server>client. I love you guys.