Machining AR-15 Lowers

Found an interesting forum post describing the advantages of machining from a forging as opposed to a billet.  45 min to machine a forging vs. over 2 hrs for a billet?

 Also, I found another place (Stillers Precision Firearms) that sells funky billet lowers for nearly $400.  If they have any in stock, that's about what regular lowers are going for these days....

AR-15 Workprints

I've run across a PDF file containing dimensions for an AR-15 lower receiver before, but then lost the link.  Recently I ran across a page containing CAD files for an AR-15 lower and DIAS (drop-in auto sear).  The former is cool, but machining a lower would be difficult and time-consuming, and machining a DIAS is felony-level illegal due to the Hughes Amendment to the 1986 FOPA.

There's also CNC Gunsmithing, that shows a bit how to do the machining with CNC, and has a few prints available.

Magpul has dimensions for an M4 receiver extension online.