with some cutting oil, a hack saw, and about 10 minutes of energy.
I first tried heat and a barrel vise that I use to remove rifle barrels....no go..and I was afraid to apply 'too much' heat.
I've flat filed the muzzle but being OC, I'll stick it in the lathe and cut the muzzle face flat. T/C said the muzzle brake was NOT designed to be removable, and I think I believe them. Stainless will gall easily and so I think even if I had applied "enough" torque the barrel may have been damaged before that MT unscrewed.
just FYI in case anyone else is wanting to be 'rid' of their MT.
