I'm also a big fan of S&W and think it is an excellent choice, with one note.
A good tolerance between the cylinder and the barrel is .004 - .006. More than this and the round loses energy as it transitions from the cylinder to the barrel. Less than .004 and the powder residue can cause binding as the cylinder rotates. I have a S&W mod 66 that measures .003. After about 50 rounds, I have to wipe it down to keep it from binding.
With this in mind, I would think that dirt and grit would have the same affect as spent powder and might cause some binding if the gun is very tight. From what I've read, most revolvers fall on the side of >.006 so its not an issue. However, just to be sure, I took a feeler guage with me the last time I bought a wheel gun. The owner looked at me like I was crazy. He may be right....my wife says I overthink stuff...
