Joe,
I'm not a pro gunsmith but have done a number of BATs and others that have the cone bolt. I've found that it is rather easy to thread the shank and then do the cone in the barrel but hold it obviously shallow. I then screw the receiver on, with the bolt closed, and allow the bolt face to touch the cone. At that time, I measure the space between the receiver and the shoulder on the barrel. That distance plus about .005 is how much more I must remove from the cone.
I have a dial indicator setup to show where the carriage was when I made the cut before trying the receiver/bolt.
Harder to describe than it is to do, I think.
There was an article in PS a few years ago on making tooling that allowed one to establish cone depth but I never saw a reason to go to that extreme.
Jay, Idaho