remove the flat head screw, place the receiver stub in a vise, put a 5/8" diameter piece of steel in the gas tube so you don't colapses it, then put a wrench on the outside of the shroud close to the receiver with the gas tube closest to the wrench body, and give it a good yank counter-clock-wise.? It'll come loose.? Like an old co-worker used to say, "you have to suprize it!" ? Good luck.
Remove set screw. Put the receiver end into a strong and sturdy vise. Spray penetrating oil down into threads. Heat and oil again. Let it cool and then put it in the freezer for over night. Take out of freezer heat shroud at base of shroud. Use thin channel locks or anything you have to get shroud loosened. I also used a sledge hammer to bust it loose. Should come right off.
