Multi-piece polymer ammunition cartridge

A polymeric ammunition cartridge having a 2 piece case comprising:

• an primer insert comprising a top surface opposite a bottom surface and a substantially cylindrical coupling element that extends from the bottom surface, a primer recess in the top surface that extends toward the bottom surface, a primer flash hole aperture positioned in the primer recess to extend through the bottom surface, and a groove positioned around the primer flash hole aperture in the primer recess;
• 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 hole aperture and into the groove to form a primer flash hole;
• a polymer nose comprising a generally cylindrical neck having a projectile aperture at a first end;
• a shoulder comprising a shoulder top connected to the generally cylindrical neck opposite a shoulder bottom;
• a nose junction positioned around the shoulder bottom;
• a skirt connected circumferentially about the nose junction to extend away from the shoulder bottom, wherein the nose junction and the skirt are adapted to mate to the body coupling;
• a diffuser comprising a diffuser aperture positioned in the primer recess to align the diffuser aperture with the primer flash hole;
• a primer inserted into the primer recess;
• a propellant at least partially filling the propellant chamber;
• and a bullet frictionally fitted in the bullet-end aperture.