Open question. What is considered today to be a safe chamber wall thinkness in fluid steel barrels? Once I saw a comment in DGJ that .097" was plenty for a 12Ga gun. More recently a review on the 28 Ga RBL in Shooting Sportsman mentioned .065" as beign sufficient. I presume that chrome-moly or chrome-nikel steels have different standards, the latter being usually 11% stronger than the former, allowing for lighter barrels in bespoke guns.