Use all weapon attachments (2)

All you have to do for the trophy is equip one of every weapon attachment which you will get if you are actively switching weapons and picking up weapons from fallen enemies (for the Weapons Master trophy).

Full Weapon Modification List:
Silencer (Triangle) - Default on SCAR
Flashlight (Square) - Default on SCAR
Laser Pointer (Square) - Default on Pistol
Tactical Attachment (Circle) - Default on SCAR
Grenade Launcher Attachment (Circle) - Default on SCAR on Chapter 6
Iron Sights (X) - Default on SCAR
Reflex Sight (X) - Default on SCAR
Assault Scope (X) - Picked up randomly throughout all chapters on FY71
Sniper Scope (X) - Chapter 3 @ the end, kill Korean Nanosuits one will drop a sniper with this attachment
Incendiary Ammo (R1) - Picked up in Chapter 4+, scattered around enemy ammo caches
Explosive Ammo (R1) - Picked up in Chapter 4+, scattered around enemy ammo caches