An ammunition article comprises a polymer cartridge case formed of a polymer composition comprising a thermoplastic polymer, preferably the polymer composition having a density of less than 1.35 determined in accordance with ASTM D792, the polymer cartridge case having a first end, an opposing second end, and a chamber disposed between the first end and the second end for receiving a propellant; a projectile attached to the first end of the polymer cartridge case; a metal base insert joined to the second end of the polymer cartridge case; and a primer carried by the metal base insert; wherein the metal base insert and the polymer cartridge case remain joined together as a single piece assembly upon loading, firing and removal from a chamber of a firearm for a polymer case temperature of −65° F. (−54° C.) to 165° F. (74° C.).