An apparatus for perforating a casing string including a first module and a second module, each including a gun assembly. The first module is positioned longitudinally adjacent the second module on the casing string. Each module contains a firing assembly for igniting the gun assembly in the first module, a remote signaler to remotely detonate the firing assembly, and ballistic transfer assembly for igniting the gun assembly in the second module. The ballistic transfer assembly includes a booster charge.