Dead Space: Extraction

This is pretty simple and refers to firing your weapons. Yes, all weapons count towards getting this. You can't fire one shot with the plasma cutter getting 100% and then use another weapon for the rest of the Chapter firing whenever you like. With whatever weapons you use you need to hit 80% all the time.

To make this trophy easier for you I would simply wait until a necromorph is right near you. This increases the target meaning you have more of a chance to land a shot.

Another trick you may want to use is with the rock saw weapon you get on Chapter 1. If using a DS3 you can constantly spam as a necromorph is near you; it basically creates a small barrier meaning you are less likey to get hit. Now as the necromorph is right in your face you can pick off your shots more easily.