the link posted above is not from a revolver. The revolver info is under the cylinder gap section.
With a cylinder gap of .006 you can see the velocity dies down much faster due to the escaping gasses. You gain about 200 fps from 2" to 6" barrel, and about the same from 6" to 18". the ratio of barrel length to velocity narrows considerably because the longer the bullet is in the barrel the more gasses can escape through the cylinder gap. You don't get that big increase like would from a Thomson or Marlin.
Cylinder Gap Test
Gun permit?? A bread crumb tossed to a sleeping society awoken by the sound of complacency. "They are for your own good", and "you will understand when you see all the lives they save". Yes master, what else will you toss me from your bag of infringements?? Do you want me to roll over and play dead? I do that very well. --skidder