Those who prefer using CO2 for the gas blow back rifles, Airsoft Buddy now has these available for the WE M4 GBBs... "WE just launched the CO2 Conversion Kit for their Gas Blow Back rifles. This kit mainly is for all existing WE GBB owner to use CO2 magazines. This kit can use regular gas and CO2 magazines. It also can make the power more stable. Please refer to the following link for product details (click on the photo below):