An apparatus for applying liquid liner to the interior of a rocket motor tube includes a horizontal surface; a rail mounted on the horizontal surface; a carriage that is movable along the rail; cartridge saddles and a bearing block mounted on the carriage; a cartridge gun disposed in the cartridge saddles, the cartridge gun including an extended tip that is longer that the rocket motor tube to be lined; a power supply connected to the cartridge gun; a rotary driven linear actuator mounted on the bearing block; a shaft drive mounted on the bearing block in operative association with the rotary driven linear actuator and in contact with a trigger of the cartridge gun; a weighing scale disposed on the horizontal surface; and a V-block disposed on the weighing scale, the V-block for holding the mask mounted rocket motor tube in axial alignment with the extended tip of the cartridge gun.