I had the worst one of my life the other day.
I had a factory armalite upper, A3, in an action block. Just trying to pop off the barrel nut to install a LaRue 9.0.
I put all my weight on the wrench, would not budge. The receiver was torquing the crap outa my action block. I was afraid the receiver might give.
Applied some heat.... no difference.
So - I applied a 4 FOOT piece of pipe on the end of the armorers wrench, and it still took a LOT of torque to crack loose.
I was amazed to see a good coating of moly grease existing on the threads. I was expecting loctite or epoxy.
When we installed the LaRue - it was the same thing.... at just snug, the barrel nut gas tube hole was just past perfect. Had to go all the way to the next one, and it got TIGHT halfway there. Had to bust out the BFH to nail this one. Luckily, this ar went home with no damage.
On that pic of the broken barrel nut - you should not use an armorers wrench for installing/removing aluminum nuts. Aluminum is too soft - you should get a YHM or GI type wrench with three lugs.