Came across a complete set of lapping tools for the AR-15, AR-10, M5E1 and M4E1. I have all 4 of these receivers so I thought I'd give them a try.
http://www.gandgrifleworks.com/AR10-Lapping-Tool-p/arlapset.htm
I'm a press operator at a small(ish) ammunition manufacturer. We have the capability to pump out around 100,000 rounds per day, which is a miniscule amount compared to those numbers. Very impressive.