An apparatus comprising a charge tube for a perforating gun assembly used in harvesting energy in a wellbore and a retaining projection formed on an end of the charge tube. When the charge tube is inserted into a gun body, the retaining projection engages with the gun body of the perforating gun assembly to restrict movement of the charge tube with respect to the gun body when engaged with the gun body. The retaining projection can comprise a plurality of collet fingers on an end of the charge tube that engage with the gun body to longitudinally retain the charge tube. The retaining projection can comprise at least one alignment finger that limits radial movement of the charge tube with respect to the gun body. The retaining projection can comprise a plurality of centralizing bend tabs that restrict radial movement of the charge tube when inserted into the gun body.