From what I've read on the forums (and packaging), the Red 271 is rated as permanent high strength. That means once it sets, it can only be removed by heating with a torch and using tools to break the bond.
I'm glad I can count on Loctite holding up, but you never answered my question...
I did notice one other thing... When I would attach the Shark Brake w/o barrel nut it would appear that my barrel extend too deep or far forward into the Shark Brake. I would think this may effect the performance somewhat. Maybe more so if you were using it for door breaching. (Not that I see myself breaching doors)
So if I back off the brake there are threads exposed on my barrel. I would say the barrel nut serves well to cover that "excess" up.
You don't think that would take away any functionality of the muzzle brake?