Conversion unit caliber .22LR. When the gas pressure forces the movable chamber backwards to start the slide on ist rearward travel. Enough energy is imparted to the slide for entire automatical reloading cycle. The movable chamber achieves the feel of the more powerful recoil which is normally expected from a larger caliber pistol. Plus models are equipped with a fibre optic sights. The whole kit includes 2 plastic magazines.