S.T.A.L.K.E.R. 2: Heart of Chornobyl

This like a lot of the grindy achievements can be obtained by finding a good spot, saving and then completing the action and loading. The game registers the action on the tracker, so it's easy to rinse and repeat. This method/guide for the drunken headshot through cover and 50 kills through cover.

Potential spoilers below.
For this,


Hope that helps!

I did this in Zalissya since there are plenty of NPC Stalkers hanging around the place. Found one near a fence and went onto the other side of it and drank some vodka. Was easy enough to line up a headshot and take the guy out.