We have tested the compatibility of the chamber in Tokyo Marui P90 TR gun. While installing the chamber, we noticed that you should exceptionally use a 21.40 mm nozzle instead of the stock nozzle, because the design of the chamber differs from the stock chamber. This will ensure the best possible seal with your new chamber. Using a stock nozzle will lead to varying muzzle velocity numbers and the gun is basically useless without changing the nozzle to a longer model.
We used AirsoftPro M4 nozzle in the test, but other same sized nozzles should also work with the chamber.