If one is planning on regularly shooting an American vintage SxS, and it has/had "short chambers," I see no harm in opening it to a standard 2-3/4" chamber AND adding longer forcing cones at the same time (assuming there is enough barrel thickness). I have had my gunsmith do so to several of my SxS shotguns.

Pressure is lowered at least marginally, and the useful life of the shotgun is probably extended. It does no harm...

gold40