2piper,
Your comments got me rethinking the whole SXS design.
If the rear lump has an active load bearing role, then the stresses are kept within the rear part of the frame and transmitted to the barrels themselves. Which raises the question about the wisdom of not allowing the whole of the action bar to come into play in countering the loads developed during firing, as would be the case with no rear lump contact.
I thought that the action bridge was there to resist torsional deformation forces rather than those acting fore and aft. As I recall there are shotguns with neither a bridge nor separate lumps, mostly folding cheap types and they seem to hold up well under hard use and minimal maintenance, as per the Bernardelli Game model. The comparison is not fair however, because most of these folders are trigger plate actions with no recesses for cocking levers, springs etc and therefore have fairly stiff action bars that can contain the stresses within each side in the absence of the bridge.
This will take some renewed analysis and gives me an excuse to start looking critically at a lot of shotguns, which is not such a bad thing!
