Hermano campero. I have a bit of 'campero' PTSD
Pollo Campero is sorta the Kentucky Fried Chicken of Guatemala, and on one of our mission trips 2 of the team members went with brother Gideons to the next town and had lunch at Campero. They returned with Norovirus and the whole team got sick! The inside bathroom was continually occupied and folks were running to the outhouse and the family dogs thought it was great fun to chase and watch the Gringos
The answer to your question illustrates why the answer is rarely simple.
The best answer is "To what service and proof pressures was the barrel proved?"1300 kg/cm² is about 18,500 psi
CIP 12g “High performance/Superior Proof” is 1320 BAR = 19,145 psi for a Maximum Average (Service) Pressure 1050 BAR = 15,229 psi
Contrary to the mythology, U.S. makers of vintage doubles DID prove their guns (using pattern welded and fluid steel tubes that had been proved in Belgium) at 16,000 - 18,000 psi
If your gunsmith calculated that pressure based on a bursting or hoop stress formula, which don't work well for unobstructed shotgun barrels, he needed to know the steel tensile strength.
Is the barrel pattern welded or fluid steel? Siemens, Cockerill or Krupp?
1.5 - 2 mm = about .06 - .079"
I assume that is the minimum wall thickness and certainly not the end-of-chamber, which we also need to know (and the 9" from the breech would be helpful also)
The gun is a 12g? What does the bore measure and is there evidence of honing or other barrel modification?
Bell ringing MAY indicate the rib is tight, but little else.
