I'm still fighting trying to get the crush washer off of my 20S 6.5 Creedmoor. Tried all the suggestions here and on Youtube with no success. Tomorrow I'll try heating it up and see if it expands enough to pull straight off or at least get it up far enough to engage a barrel thread and twist it off with a pipe wrench. As it is now, it freely rotates but is so close to the barrel shoulder below that there isn't even enough room to work a very thin blade flat screw driver in between the shoulder and the back of the crush washer. Even if you could, I'm pretty sure that the blade would snap off immediately on trying to work it up or down.
Worse come to worse I've considered placing the barrel muzzle end up in a vice, wrapping the threads well with tape or slip a plastic/rubber tube over the threads and then very slowly have at the muzzle end of the crush washer with a hack saw with a very fine pitch steel cutting blade going ever so slowly. I have a Dremel tool that would make fast work of it but I definitely don't have a steady enough hand to not screw everything up with the Dremel. How in the hell FN first installed the crush washer is beyond me. I've got to believe it was heated and then installed as there's no evidence whatsoever that it was screwed on the barrel threads prior to installing the Surefire Pro muzzle brake.
I'll happily entertain any ideas that those way smarter than I am and/or any machinist's on the forum might have. I've got a Surefire shoulder ring coming from PMM in a few days and then I'll be installing a YHM 4302 5/8x24 QD flash hider and a YHM Resonator R2 .30 cal suppressor. Like everything in life, it's the smallest things that are the most irritating and frustrating. I'm damn tired of wasting an unknown number of hours each night analyzing how to remove this *** thing instead of getting my much needed beauty sleep.
I feel much better now that I've vented. Thanks for reading and any suggestions other than sawing off the barrel and having it rethreaded will be VERY appreciated. Anybody that can solve this conundrum (relatively easily) can surely cure cancer...