[KevinG]

Thanks, Kurt, but I guess I wasn't clear. The allen head socket part of the barrel nut is fine, it's just filled to nearly the top with the exhaust head stud. Picture trying to remove a nut without the flats - that's what I am facing.

It's too tight in there to get vise grips or channel locks on the nut, and I am afraid of damaging something if I try to gain purchase on the barrel nut with a cold chisel so that it can be backed off.

I guess what I'm really looking for are some successful BTDT stories.