Killed the first guard in Depot
Metro 2033 Redux RAIDER – Achievement / Trophy Guide
In the beginning of Depot you will be on a railcar, equipe a long range weapon and use the military grade ammo just to be sure. After the car makes 2 turns, the trackline will go straight. Shoot straight ahead and kill the first guard. He is hard to make out, but you can see by the hitmarkers that he is walking right in the middle of the tracks.
He doesn’t have to be killed silently like the achievement says. Just make sure you kill him as soon as possible, before he can join his buddies.