This allows for almost any ranged firearm to be customized to fit the player's character build. Grip mods create pistol weapons, while stock mods create rifle weapons.

Most firearms, including energy weapons, offer the option to customize the grip/stock, receiver and sight, changing which perks affect the weapon.

The Blacksmith perk is used to create better modifications for melee weapons. The Science! perk is used to create better modifications for energy weapons and create advanced modifications for bullet based firearms. The Gun Nut perk is required to create better modifications for guns. There are over 700 mods, generally including sights, barrels, stocks, receivers, magazines and more. Weapon mods can be built from raw materials and attached to weapons at weapons workbenches.