Mach Sakai does a comparative review of Non-Freon Gas And Freon Gas for use in gas blowback guns in this video. As for the airsoft gas blowback pistol that he uses for the review, that's the Tokyo Marui Biohazard Lightning Hawk .50AE 10inch Magnaport Custom Gas Blowback Pistol that can also be converted back to a regular Desert Eagle .50AE gas blowback.