MAS 49/56 Muzzle Brake

I need to remove it to get the grenade-launching ring off the barrel. I can get both pieces of the brake to move together on the barrel but can't get the rear lock nut to unscrew. The threads are RH. There is a lock washer between the brake and the lock nut but obviously there has to be a way to get the thing off. At the risk of ruining the parts, I have already used two big vise grips - one turning the nut left and one turning the brake right, This accomplished nothing. Neither piece is Loctited to the barrel because as I said, I can turn them both together about 20 degrees either way. I also know I should use a pin spanner for the lock nut, but don't have one. How about the brake? No tool-engaging surfaces are evident. If I had the right spanner for the nut, it might also fit the vent holes on the brake, I suppose. The slot you see on the lower front of the brake is the bayonet stop and there is not another one at 180 degrees. So, anybody who has taken one of these off, tell me about it!
Something just occurred to me - is it possible that you have to dig the deformed washer out of the locking slots first?
https://www.milsurps.com/images/impo...s49565cs-1.jpg

Okay, I 'unstaked' the washer but it still didn't break loose. Now I'm treating the nut/washer/brake interface with penetrant. This is a tough cookie!

Got it. I went back and improved my 'de-staking' of the lock washer, and let the 'Sili-Kroil' work for a few days. This time it came off easily and I got the grenade range-finding ring off. I do have some plier marks on the flash hider and lock nut but I'll work on that and reblue.

BTW, I know most guys know and use 'Kroil' by Kano Labs, but their 'Sili-Kroil' does everything 'Kroil' can do better.

I'm curious, why you need to get the ring off?