Available right now at eHobby Asia are the A.P.S. (Hakkotsu) APM50 M40A3 6mm Rechargeable Cartridge. This is a 6mm Rechargeable Cartridge designed (patent pending) for the APS APM50 Sniper Rifle use. design of this cartridge has patent. The gas won't leak by accidental drop and it is relatively safe compare to similar cartridge system found in the market. 

No Spring is used inside the cartridge, all the power and pressure are done by O-Ring and valve only.  Maintenance is easy and simple and there is Engraved White Color Marking depending on the design you order. 6 high speed cartridges are include in this pack.