I have done what Bob did. I shaved the tubes down until they fit the chambers. Used to be that Briley would not fit 20 gauge tubes with choke tubes if the 12 gauge gun was choked tight. The alternative is to order 28 gauge tubes or get them to make the 20 gauge tubes terminate before the chokes in the 12 gauge gun. The shorter tubes are probably better balanced anyway. The 20 gauge extractors are very thin and fragile, a problem the 28 gauge tubes don't have.