A two piece, two-stage, reduced-energy mechanically operating cartridge is provided for launching, a configured bullet choice of various compositions from a dedicated or modified firearm. The cartridge unit is comprised of a primary case having a cavity to receive a propellant unit or propellant connection and a piston sleeve having a cavity to receive the configured bullet choice, the primary case coupled to the piston sleeve. The cartridge having a retracted pre-firing state and an expanded fired state whereby the piston sleeve and primary case telescope apart forcing, the firearm's slide or bolt to the rear, a mechanical operation opposed to a conventional cartridge with gas blow back operations.