Firearms in "The Book" have a base version and two successive upgrades that add addons. Each addon modifies the weapon's functionalities and increases its effectiveness in combat.
For example, the Gatling Gun, after the first upgrade, has a faster charge time and generates secondary explosions if the enemies hit are under the effect of the grenade. The second addon allows the Gatling Gun to restore the character's health during combat.
Finally, crafting allows the tier of each weapon to be increased (from 1 to 5), enhancing its base stats such as damage, range, and fire rate.