Thanks to both of you! I do indeed have a copy of John's CD (my first and only activity two years ago was to get a copy of it) and have been studying them like any good scholar should. I'm fully tooling up for this project: Inserts, cutters, reamers, gauges etc. so that i may make more in the future. I've managed to locate a properly sized rounding cutter to make the cut, but have not yet purchased it.
This site has a 1.4x2R Corner rounding tool, which I would cylindrically grind to 5.1mm, and surface grind the tip to a diameter of 1.5mm. Should be a fun project
Fortunately a good friend of mine is not only a gunsmith, but a rifle barrel maker. He's got all the fun equipment to make the project go. Even got my barrel: a 32" blank of 4150, .308 cal, 1:10 twist.