The S-System has long upper rail, side rails and bottom rail that can accept both airsoft and real accessories. Rails are metal made while the system frame is plastic. The method how the S-System is locked to the gun is simple and well functional. Given the functionality of S-System battery exchange is relatively easy. Unlike in the M4 RIS this time the battery can be stored inside S-System and special wiring is provided with the gun to faciliate this. As in real SIR-system the S-System has holes across its body to allow re-positioning of rail units. Both flip up sights are fully adjustable and the rear sight is secured to low profile position with help of side lever. Similarly front flip up sight has release button to allow positioning to low profile position