A perforating gun may include a first housing, a charge holder positioned within the first housing and configured to receive a shaped charge, an initiator, a detonating cord configured to detonate the shaped charge, and a first spring positioned within the first housing. A relative position of the initiator and the detonating cord may be movable between a first position in which the perforating gun is ballistically unarmed and a second position in which the perforating gun is ballistically armed. The first spring may bias the initiator and the detonating cord to the first position.