Agent A: A puzzle in disguise

Missable

This will be done in Chapter 5 and you'll need Security Clearance Level 5 to get it. Once you have the appropriate access, use the elevator to go down to basement level 2 (Floor -2). Interact with the room straight ahead to go inside. You'll notice there are 4 lights hanging down, the 3rd of which is blinking. Interact with this light to reveal the armory. Zoom in on the right wall and there will be an ammunition clip on the lower right shelf. Pick it up.

Head back to the elevator and go back to the ground floor (Floor 0). Go inside the door just to the right of the elevator (with the "2" panel next to it). Interact with the gun inside the run and place the ammunition clip inside the gun. Spam on the trigger so you fire the gun a total of 100 times, unlocking the trophy.