cartridge ejector(n = noun.artifact) ejector - a mechanism in a firearm that ejects the empty shell case after firing;
is a kind of mechanism
is a part of gun

ball cartridge, cartridge, cartridge belt, cartridge brass, cartridge clip, cartridge extractor, cartridge font, cartridge fuse, cartridge holder, cartridge paper, cartridge remover, centerfire cartridge, ejector, ejector seat, font cartridge, ink cartridge, tape cartridge