These rings around the barrel...
...are an unfortunate manifestation of what I consider to be poor finishing.
In the seventies I did nothing but kits and I have seen them with and without the ring.
Recently I encountered a ring in a revolver that I think began life as a kit and it was from ASM. (Brass frame)
I was very disappointed to note that ring because it provides evidense to support the charge of low quality of ASM revolvers which is a reputation which I think is only partially deserved when you compare other pistols from the ASM period.
When you examine this ring closely on a kit which is untouched, you can almost see where the lathe stopped it's advance. Kit builders are well advised to finish the barrel such that the ring disappears. It takes a little time with a flat file on the top and sides and with a half round on the underside just forward of the lug.
Then wrap sandpaper around the file and repeat the process.
Then go to hand sanding.
My reading of history convinces me that most bad government results from too much government. Thomas Jefferson