Before we start deleting files, it is important to understand why the guns aren't working. In a vanilla Starbound installation, gun issues are rare. In a modded environment, specifically with FU, the causes usually fall into three categories:
when you click, or does the character stay completely still? Starbound Frackin Universe Guns Not Working Fix
If you use the RPG Growth mod alongside FU, check your settings. Enabling "Classic Mode" in RPG Growth can accidentally disable your ability to deal damage with certain weapons. 2. Hunting Down Mod Conflicts Before we start deleting files, it is important