You need to mate barrel nut threads with upper receiver threads - thread mating, on two separate parts, usually of two different materials. You NEVER do that with dry threads, because you'll gall the fuk out of them, and they'll seize. Even if it's the SAME material, its never, ever good - I've galled enough stainless-only and aluminum-only hardware to tell you that's the truth.
I'm shocked that dude even said that - he needs slapped, and I'll say that publicly... What a dumbass...
FOr barrel nuts - if you've never heard this yet- you don't tighten it and forget it. Torque it once, WITH GREASE, loosen it. Hit again for #2, and loosen it, hit it again for #3, and SET IT. You do this THREE TIMES before you set it down to torque...