I am looking at a 686+ and was looking down the cylinder and saw what looked like there was a ring near the end and I was wondering if this was part of the cylinder or just very dirty.
Thanks Steve
That is just the step at the beginning of the throat. If the example that you looked at was used extensively with .38 Specials, and not cleaned well, it may appear to be wider, more pronounced, as carbon builds up where the shorter .38 case ends and the throat (for .357's) begins.