I am in the unfortunate situation that the "extra" set of barrels fit like they were made for the gun, even though it was an extractor set and the originals were ejector. I didn't have to do any work to make them fire, but a talented gunsmith made them extract while the original barrels ejected. Only the original ejector forend was used. I have no idea why these two sets of barrels were so closely fitted (without fitting). I am only mentioning my experience so other readers will realize that such situations may exist.