Customize a weapon to use all 5 modification points

Customize your weapon by holding down the SELECT button and equip weapon mods via triangle, circle, square, X and R1. The first time you'll be able to get this trophy is on chapter 4 because you are unable to equip specialty ammo until you are that far in the game. You can find incendiary rounds when you're going around taking out the AA guns, the other attachments are basically a given as you start with a default on every other slot.

I got this trophy with the FY71 with this configuration:
Incendiary Ammo (Magazine), Silencer (Barrel), Tactical Light (Side Rail), Grenade Launcher (Under-Barrel), Reflex Sight (Rail)