If I were in your situation - I'd remove the barrel from the house and store it someplace far away while looking for a replacement barrel.
You can write to the ATF asking for a definitive ruling, but you're obviously asking for trouble since I fully believe you've made a boo-boo here.
I've written to the ATF and have generally received courteous and informative responses.
JYD #123 The great one formerly known as Architect.
I am now a fictional British television police officer (currently a Detective Sgt) at Thames Valley Station. My governor is Detective Inspector Fred Thursday and it’s 1969.