Technology is amazing.
See http://defcad.org/ for some interesting pictures, plans and notes.
For the AR-15 mag, the notes are at http://defdist.tumblr.com/post/40315167419/defdist-printed-ar-mag-part-i
and are great reading.
The plans are at http://defcad.org/wp-content/plugins/download-monitor/download.php?id=50
Enjoy.
Theophilus