Part 2 of this series, "AR Pistols vs NFA Short Barreled Rifles" is here: https://www.full30.com/video/cedf78ff134d2408a40fbcb9c021dd6e
This should have been titled: "Everything you always wanted to know about owning a machine gun but were afraid to ask". (If you are as old as I am you will understand that joke. :-)
This video goes into the ownership of machine guns and the paperwork necessary as well as auto-sears, (DIAS and Lightning Link) and the Slide-Fire alternative. It explains why they are so expensive and how come we see new ones, when we're told new ones are not allowed, all over the internet and television.
Slidefire Stocks here: http://www.slidefire.com/