A safety device for deflecting spent ammunition cartridge cases away from a rifleman as they exit the ejector port of a semiautomatic or automatic rifle. In a first embodiment, intended for use with a rifle from which the carrying handle has been removed from the rifle's upper receiver rail in order to mount a monocular night vision device or other rail-mountable device, the deflector includes a deflector plate pivotably attached to a base plate and movable between a lower, ejector port covering position and an upper, ejector port uncovering position. A thumb-screw adjustable clamp attaches a front end of the base plate to the rail. A rear wall attached to the base plate has a rocker arm mechanism for alternately capturing the deflector plate in the lower position and releasing it to move to the upper position. A second embodiment has two spaced-apart clamps attached to a base plate for attaching the deflector to a rifle's carrying handle, but is otherwise similar to the first embodiment.