Originally Posted By racerpk11:
3dcontentcentral.com has just about everything I believe.
A quick search for "ar-15" there provided a wealth of data. Many more parts than just lowers. I didn't look beyond page 1, but judging by what was there I'd guess that site has schematics for almost everything short of a barrel, well at least the barrel rifling (that requires special tools beyond a CNC).