Erik Cortina made a video two years ago that is the nicest I have ever seen for modifying cases for use with the Hornady (Formerly Stoney Point) OAL gauge. Here is the URL address:


http://bulletin.accurateshoote...hornady-o-a-l-gauge/

I found the "L" sized letter drill at McMaster Carr, and also at Amazon.
The 5/16-36 tap was only available at Amazon.
No big surprise, but the "L" drill, and 5/16-36 tap were not available from Brownells.
I went for HSS for the drill bit, and also for the Tap.
They will hold up well in the brass of the cartridge case.
Erik used a hobbyist, table top mini lathe to drill out the primer pocket at ~ 400 RPM. No lubricant is used.
He also used the lathe to tap the brass, this time at 100 rpm.
All in all, it is a very clean process.