A perforating tool assembly may be modularized by providing modular charge segments to provide for multiple configurations of shaped charges without the requirement of excess inventory. The modular charge segments may comprise any number of modular charge holder segments and modular charge spacer segments which are configured to provide for different spacings and offsets of shaped charges disposed within the modular charge holder segments. The modular charge holder segments include slots and locking tabs to allow for the differing offsets between charges. The modular charge holder segments may comprise a slit that allows the modular holder segment to be flexed or deflected to permit the loading and downloading of shaped charges. The modular charge segments may comprise a plastic or rubber material to provide for safer deployment of shaped charges downhole.