Keep in mind that if you do not have an air-tight connection from the main barrel to the tubing you are installing in the faux barrel, this will actually cause worsened ranges rather than improved.
Since you mentioned it, I decided to take apart my Retaliator (which was a pain BTW) and realized that there was an opening in the breech where the dart tooth sits in the primed position. I suppose this will be a problem. Do you think that taking out the AR and adding an upgrade kit would get the air pressure high enough to cause the air to "clog" the gaps in the breech until the dart can leave the barrel?