The more recent AEGs from ARES Amoeba series use their updated gearbox with the electronic control unit inside. This particular control unit is allows the user to alter the method of which their M4 AEG shoots. The standard M4 has a safe, semi auto and full auto fire selector but what the control unit allows you to do is allow you to shoot in either, Semi / Burst, Burst / Full Auto, or Semi / Semi as well.

Since this is a a version 2 gearbox, it will fit in MOST brand M4 AEG as all gearboxes are relatively the same shape and size. This is because some G&P and VFC bodies change depending on the model so there may be need for some modifications. For you to alter the fire selecting mode, you will also need to purchase the ARES Electronic Firing Control System.