Michael,
You deftly played the chords of my heart when spoke of the MAC 10 on today's podcast! I have two of them (45 and 9) and they are "Powder Springs" models. I put collapsible M4 stocks on them (plus I have Gemtech suppressor for the 45) which makes them easier to control. I clocked mine at 900 and 1000 rounds per minute.
One other site you want to check out is Lage Mfg (
http://www.max-11.com/) and check out their work, which I hear is really first rate. They make uppers that slow the cycle rate to a more manageable pace on these guns.
Thank you for covering this weapon today!
-FullAuto