Liquid CO2 working its way into your BT-4 marker's valve causes velocity spikes and poor gas efficiency. Expansion chambers help eliminate this by giving the CO2 room to expand, resulting in more consistent velocity (very important for accuracy) and more shots per fill. The BT-4 Magazine Expansion Chamber not only helps your BT-4's performance but gives that mean milsim look and feel of an M16/ M4 magazine. Now your marker can look AND shoot better!

Item # XCBXCM16