COLLECTABLE and MISSABLE
There are a total of 10 weapons in the game that count towards this trophy, 4 of them are added automatically to your inventory (Jill´s Survival Knife and G19 Handgun, Carlos´ Combat Knife and G18 Handgun), 2 of them are throwable grenades you find (Hand Grenades and Flash Grenades), and 4 of them need to be hunted during the game. Keep in mind that the weapons bought from the in-game shop, however, do not count towards the trophy.
Since it's far less possible to miss grenades, you should only focus on the location of the 4 weapons you must find during your playthroughs:
- M3 Shotgun: At the Subway office (behind the door next to where you find the Fire Hose). You need the Bolt Cutters to open the case where it is stored. If you miss the Shotgun here, you will find it before leaving the sewers at the last safe room.
- MGL Grenade Launcher: After sliding down the Sewers to the Lower Waterway, you will come across a split path, follow the left one until you get to a small ladder which leads into a safe room. The Grenade Launcher is inside this room. If you miss the Grenade Launcher here, you will find it before leaving the sewers at the last safe room.
- G18 Handgun (Burst Model): As soon as you regain control of Jill during the Hospital section of the game, check the table next to the door.
- .44 AE Lighting Hawk: After you regain control of Jill during the Hospital section of the game, head to the 2F of the Hospital, there, you will find a hallway with some rubble only Jill can squeeze under. Behind it, you will find a window you can drop down from to reach the 1F Courtyard (technically the same place you found the Locker Room Key with Carlos). In this place you will find a box with the Magnum inside.