Polymer ammunition and cartridge primer insert

A polymer ammunition cartridge comprising:

• a primer insert for comprising a top surface;
• a bottom surface opposite the top surface;
• a coupling element that extends from the bottom surface, wherein the coupling element comprises an interior surface and an exterior surface, wherein the interior surface comprises:
• a transition region that transitions from the bottom surface to a second segment wherein
• the transition region has a radius of from 0.03 to 0.05 inches;
• a first segment extending from the second segment and terminates at a tip, wherein the first segment has a first segment distance from 0.02 to 0.18 inches and
• the second segment has a second segment distance from 0.02 to 0.18 inches,
• wherein the second segment has a second segment angle from +3 to −3 degrees relative to a first segment angle of the first segment wherein the first segment angle is from +6 to −6 degrees from perpendicular to the top surface;
• a primer recess in the top surface that extends toward the bottom surface;
• a primer flash aperture positioned in the primer recess through the bottom surface;
• and a flash aperture groove in the primer recess and positioned around the primer flash aperture and adapted to receive a polymer overmolding through the primer flash aperture;
• a polymeric middle body comprising a polymeric body extending from a body coupling over at least a portion of the primer insert, wherein the polymeric body is molded over the cylindrical coupling element and into the primer flash aperture and into the groove to form a primer flash hole;
• and
• a polymer nose comprising a generally cylindrical neck having a projectile aperture at a first end;
• a shoulder that extends from the generally cylindrical neck;
• and a nose junction in communication with the shoulder, wherein the nose junction is mated to the body coupling.