A method of making a composite ammunition casing, said method comprising: overmolding a removable core mandrel with at least one polymer or polymer-forming material, the at least one polymer or polymer-forming material forming a polymer shell in contact with an outer profile surface of the removable core mandrel; and separating the removable core mandrel from the polymer shell to form the composite ammunition casing; characterized in that said composite ammunition casing consists of a polymer shell and an overmolded metal bushing having a primer pocket and a hole that connects the primer pocket with a powder chamber of the polymer shell; in said overmolding step, a portion of the removable core mandrel is overmolded with the at least one polymer or polymer-forming material; said overmolding step further comprises overmolding at least a portion of each of one or more mold inserts, wherein at least one mold insert comprises the metal bushing, with the at least one polymer or polymer-forming material, the at least one polymer or polymer-forming material further being in contact with an external surface of the overmolded metal bushing; said separating step comprises (i) reducing a cross-sectional outer mandrel dimension of the removable core mandrel from an initial cross-sectional outer mandrel dimension d omi to a final cross-sectional outer mandrel dimension d omf so that the removable core mandrel passes through an internal opening within the polymer shell, the internal opening having a cross-sectional opening dimension d o with d omi > d o ≥ d omf, and (a) an outer surface of the polymer shell provides an external shape (i) according to an ammunition caliber and (ii) of a cartridge comprising a cartridge body, a cartridge shoulder and a cartridge neck, (b) an inner surface of the polymer shell (i) forms a projectile adjustment area and the powder chamber, (c) the overmolded metal bushing represents an overmolded end component of said composite ammunition casing, and (d) an inner diameter of the powder chamber formed by a central core mandrel and a set of one or more connectable mandrel blades mounted on the central core mandrel of the removable core mandrel with the initial cross-sectional outer mandrel dimension d omi being greater than (i) the cross-sectional opening dimension d o and (ii) a cartridge neck inner diameter. overmolding a removable core mandrel with at least one polymer or polymer-forming material, the at least one polymer or polymer-forming material forming a polymer shell in contact with an outer profile surface of the removable core mandrel; and separating the removable core mandrel from the polymer shell to form the composite ammunition casing; characterized in that said composite ammunition casing consists of a polymer shell and an overmolded metal bushing having a primer pocket and a hole that connects the primer pocket with a powder chamber of the polymer shell; in said overmolding step, a portion of the removable core mandrel is overmolded with the at least one polymer or polymer-forming material; said overmolding step further comprises overmolding at least a portion of each of one or more mold inserts, wherein at least one mold insert comprises the metal bushing, with the at least one polymer or polymer-forming material, the at least one polymer or polymer-forming material further being in contact with an external surface of the overmolded metal bushing; said separating step comprises (i) reducing a cross-sectional outer mandrel dimension of the removable core mandrel from an initial cross-sectional outer mandrel dimension d omi to a final cross-sectional outer mandrel dimension d omf so that the removable core mandrel passes through an internal opening within the polymer shell, the internal opening having a cross-sectional opening dimension d o with d omi > d o ≥ d omf, and (a) an outer surface of the polymer shell provides an external shape (i) according to an ammunition caliber and (ii) of a cartridge comprising a cartridge body, a cartridge shoulder and a cartridge neck, (b) an inner surface of the polymer shell (i) forms a projectile adjustment area and the powder chamber, (c) the overmolded metal bushing represents an overmolded end component of said composite ammunition casing, and (d) an inner diameter of the powder chamber formed by a central core mandrel and a set of one or more connectable mandrel blades mounted on the central core mandrel of the removable core mandrel with the initial cross-sectional outer mandrel dimension d omi being greater than (i) the cross-sectional opening dimension d o and (ii) a cartridge neck inner diameter. (a) an outer surface of the polymer shell provides an external shape (i) according to an ammunition caliber and (ii) of a cartridge comprising a cartridge body, a cartridge shoulder and a cartridge neck, (b) an inner surface of the polymer shell (i) forms a projectile adjustment area and the powder chamber, (c) the overmolded metal bushing represents an overmolded end component of said composite ammunition casing, and (d) an inner diameter of the powder chamber formed by a central core mandrel and a set of one or more connectable mandrel blades mounted on the central core mandrel of the removable core mandrel with the initial cross-sectional outer mandrel dimension d omi being greater than (i) the cross-sectional opening dimension d o and (ii) a cartridge neck inner diameter.