All the Victory models I have seen have 2 1/2 to 2 9/16 inch chambers. They are a very thick barreled heavy gun. There was plenty of metal to open the chamber and forcing cone to modern dimensions on the guns we had. A well taken care of or little used Flues should last several life times. The're trap guns, designed to shoot tens of thousands of times. They were called Victory models to try to sell them to returning GI's. We had victory gardens, victory cabbage, etc.
Tom Dulin