Actually, if you go through the
Revolver Checkout List mentioned by
OneInTheChamber, you'll see it. A clean barrel makes the task easier. The ring is exactly that, a slightly enlarged area in the bore. It is seen as a dark shadow in the barrel interior, usually all the way around but not necessarily.
A barrel ring is also detected in cleaning the bore, using a tight-fitting bore brush or patch. After any gross leading streaks are removed, the patch or brush should push through with a more-or-less constant pressure. One should be suspicious of any momentary lessening of the pressure needed to send the rod down the bore. Frequently, especially with a lighter-profile barrel, the ring may be seen or felt on the exterior of the barrel.
If a barrel ring is found, the only real cure is barrel replacement. Sometimes, a barrel ring may cause little or no effect on the shooting of the firearm, depending on several factors - - Location in the barrel, depth of the ring, type load to be subsequently fired. Most shooting enthusiasts are not content to tolerate a ringed barrel in a high quality arm, but this is personal preference.
Best of luck - -
Johnny