Using moon clips is a way to quickly reload a revolver in speed shooting. It was originally devised as a way to shoot a rimless caliber in a revolver,, and nowadays some folks are doing custom jobs on other guns such as 38 spls, 357 mags etc.
Some folks mistakenly believe you can use the moon clips with a rimmed caliber, OR still fire the same ammo w/o the clips. They seem to forget that once you shave off the rear of the cylinder, to allow the use of moons,, then the cylinder is further away from the firing pin. If you try to shoot something w/o the moons,, in most cases,, you will not get reliable (if any at all) ignition. A firearm that is modified to use moons will be permanently dedicated to that method of shooting.
As for the ATF tax stamp,, as far as I've heard,, (and I have a class III dealer friend,) it's still a one time thing.
Silencing a revolver isn't an easy thing to do as noted by the above posting about the noise/blast at the cylinder/barrel gap.