Polymer ammunition having a MIM primer insert

An ammunition cartridge engaged to an injection molded primer insert, the ammunition cartridge having a mouth that opens into a cartridge body, the cartridge body enclosing a propellant chamber and having a coupling region opposite the mouth that is configured to engage the primer insert, the primer insert comprising:

• a top surface opposite a bottom surface having a cylindrical coupling element extending away from the bottom surface, the cylindrical coupling element defining an interior surface and an exterior surface;
• a primer recess defined through the top surface and in communication with the propellant chamber via a flash hole defined through the bottom surface;
• and
• a flange extending circumferentially about an outer edge of the top surface and one or more protrusions defined in the exterior surface and extending vertically from the flange to the bottom surface;
• wherein the coupling region is molded over the cylindrical coupling element, into the interior surface to form a propellant chamber bottom surface, over the exterior surface to cover the one or more protrusions, and to the flange to secure the cartridge body to the primer insert.