I had the same issue! Keep bugging Green Mtn! stay on the line till you get someone then tell them the trouble. They will send you a paid UPS tag to ship it back and they'll re-breech the barrel. Tell them you DO NOT WANT A HELI-COIL! It'll take 6-8 weeks but you'll have your new barrel in proper working order with nothing more out of your pocket.
I know it's disapointing,,cruse back about two years in this very forum and you'll see a better explanation of it all. Short story is; they drilled the wrong hole in a large batch of breech plugs,,the new president of GMB came from the areo space industry and made the call to install stainless steel heli-coils.
I'm suprised to hear your story, i'd have thought by now they would have made the repairs proir to shipping, I had also heard some place that they had stopped production of smoothies.
Good luck friend, My heart goes out to ya,,I saved for some time to buy my barrel, and was anxious to "do some shootin" when I got it! Then I spoted that heli-coil!