We have been warned against using Pattern Welded barrels by Industry experts since SAAMI passed this resolution March 26, 1937:
“That an appropriate warning label be placed on all boxes containing smokeless powder shells, cautioning the consumer against using them in short chambered guns and also in guns with Damascus barrels and guns not in first-class condition.”
“These shells must not be used in guns with Damascus or Twist Steel barrels” warning appeared on shell boxes shortly thereafter.
RST boxes state: "To prevent injury to shooters or bystanders, use only in modern shotguns (not Damascus twist barrels, etc.) with proper gauge, load, and chambers."
SAAMI continues that warning; see p. 12 & 13
http://www.saami.org/PDF/FAQ.pdf Those of us foolish enough to ignore that warning can not then hold a dealer responsible for our foolishness.
HOWEVER - should a piece of shrapnel from my damascus barrel penetrate the skull of my friend (or grandchild) leaving them bed-ridden and mute for the rest of their not-much-of-a-life, I will most certainly be held responsible.
The hard question is "What exactly IS my obligation to assure the safety of barrels which have been deemed by experts to be intrinsically unsafe?" and does "But a gunsmith said 'Should be fine with light loads.'" represent due diligence?