Fortress Channel show the Chamber Tune they developed for the Japan version of the SIG Air P320/M17 CO2 Blowback Pistol... "We have released a "Chamber Tune" for the SIG AIR / Parabellum gas blowback M17/M18 series! Improve the ballistic performance that is not enough with the original, experience the hard CO2 blowback, and finish it into a practical handgun for airsoft use! Compatible models: SIG AIR P320 M17 (metal slide) SIG AIR P320 M18 (metal slide) SIG SAUER Proforce CO2 gas blowback P320 M17 (Japanese specification) Parabellum M17 series (negotiable)."