These Magpul Dummy rounds are made from a Proprietary hard polymer. These rounds are built to 5.56mm spec, and are useful for a wide variety of applications. Magpul's dummy rounds were initially designed to stand in as a takedown tool. Since many components, like receiver pins, Masada handguard pins, and XTM rail panels, require the tip of a 5.56mm round to disengage, the dummy rounds are ideal as a punch or press as a safe alternative to live 5.56mm rounds.
Additionally, these rounds can be loaded into a magazine and chambered into a rifle. Use the dummy rounds as failure drill initiators. When your rifle chambers a fake round, it will provide the opportunity to run a failure drill, with the dummy round being chambered and extracted.
Alternately, drill a small hole and use a dummy round as a keychain.