I keep a 20ga Flues here to remind me how gun peddlers like to ____the unwary. $450.00 tuition payment.
Paper thin to start, then honed to useless ness. I'm not shooting it.

Then, since I didn't learn the first time, I bought another at auction, hoping the barrels would bail me out. ha! The left
tube was crudely sleeved at 12 inches, and just so happened, was photo'd from the right side.
No returns.

Recontouring 20ga Flues barrels will be like repairing used aluminum foil.
Buy a NID.

Out there doing it best I can.