Do It Yourself link for making your own barrel nut wrench, including barrel removal instructions.
Smith & Wesson M&P15-22 - 5 . For those who wish to buy a steel barrel nut wrench you can find them in the 15-22 Specific CLASSIFIEDS here:
*** 15-22 Specific CLASSIFIEDS ***
Note: Several Forum members have reported the barrel nut loosening. Keep this in mind for general maintenance and inspection. Be careful to not apply a great deal of force while removing/installing flash hiders or barrel nut if you are not using a barrel vice. It is possible to break the receiver.
Forum member tips:
Belt_Fed suggests a small drop of fingernail polish will keep the barrel nut from loosening while still being able to easily remove when needed.
DasFreik puts a dot of Liquid Paper on the outside of the barrel nut so he can easily see if it has turned.