The Tokyo Marui M870 is Japanese born and bred. It’s performance, unwavering, so long as you are using duster gas or HFC 134A. Unfortunately, no one uses that outside Japan as Top or Green Gas is the way to go. That being said, the M870 can’t stand the pressure of which it is put under when using higher pressure gas, but that is all about to change. The SAT High Performance Output Valve is made specifically for the M870 from Tokyo Marui with the original stock and NOT for the G&P or Angry Gun stock modifications as there are leaking issues. This will allow you to use Green Gas with no problem and also boost the FPS up to around 360! A very simple and easy upgrade for those looking to boost performance for outdoor games.