Viggo I do actually belive they have done the opposite.
First machined the frontsight band and dovetail out and thereafter indexed after that.
That would likely save some work with problematic setups and also be more uniform barrel after barrel.
I nclude a pic here on a barrel in the lathe, this barrel is not indexed but could easaly have been indexed with at tool against the spindle.
Just my opinion.
Regards HÃ?Â¥kan
http://www.vapensmedjan.com
http://boards.rennlist.com/upload/Barrelturning2.jpg