Over the years I have observed dozens of SXS being retightened. In every case the barrels had to be smoked in to achieve a tight fit to the breech face. Smoked in means that the barrels were set back enough to require this operation. That seems to involve some rearward displacement of the barrels and I would think enough to eliminate draw contact between the rear lump and the bridge.
Some makers foresaw this problem and made provision for it. Blaser, Verney Carron, high grade Baikal OUs, Parkers, and maybe a few others, have replaceable "shoes" that can be changed to maintain contact. The idea is so simple that one wonders how it escaped the "best" makers.
Conceivably such a set up can be retrofitted to any SXS and make it infinitely repairable. It was fitted to my exprimental 3D printed prototype and it made fitting a piece of cake as it rendered the process a linear, one-surface-at-a-time business.
Modern Purdeys have a replaceable draw. Not sure of implementation serial or date.
DDA
