I have a 20 ga damascus A&N with .075" at the end of the 2 3/4 chambers proofed in England to 950 bar and I have shot it with RST low pressure a few times. I have Briley tubes in 28 ga for it to feel a little safer although the tubes are aluminum except for the chambers which are steel. I think this is extreme as is DAM's 16 ga.
My Ruger Gold Label measures .15" at the end of the 3" chamber.