I don't think it should be getting the range you say it gets. The stock valve is meant for a slow leak of air to power a continuous piston, not a rapid release of air.
From the looks of it, I don't believe he removed the piston. That black part appears to be the part right between the barrels and the piston. Since RF20s and the like have lots of air loss due to the rotating barrels without proper seals, he could be right. 50' does sound more reasonable though.
Nice mod though. Consider finding a way to band the piston like some people do in Magstrikes to get even more air from each shot. This is a good example of what I'm talking about. Not sure if there's a good place to do it in the RF20 or not.