That ring is a result of the "thread choke" which is extremely common in S&W barrels. That is why it is at the point where the barrel and frame contact each other. Don't worry about it, it is normal in S&Ws to see this if you look closely enough! It is not a "ringed barrel", and is not a result of damage! It is a manufacturing issue!
Notice my "Sig Line", I have been looking at these things for more years than most of you have been on the Earth!!
It isnt constricted in the ring, the jag with a tight patch flies through the ringed Area with no friction indicating it is an internal bulge.
I also hoped at first that it was a thread manufacturing issue, but the jag patch test proved me wrong