An extruder unit (22) for an injection molding system (20) includes a piston (48), slidably located within a piston chamber (42), and is movable between a retracted position and an extended position. The piston (48) is further adapted to rotatably mount a screw (30). A motor assembly (36) is mounted to the piston housing (40) and operable to rotate the screw (30). The piston (48) is translated by a hybrid injection actuator (38), the hybrid injection actuator (38) including: a drive unit (50) operable to move the piston (48) between the retracted position and the extended position; and a gas pressure unit (93), operable to provide a boosting force to the piston (48), thereby urging the piston (48) towards the extended position.