My heartfelt compliments as to your attention to detail and especially your endurance! You are an engineer?
There are wall thickness recommendations here, with a link to a previous thread on this forum
https://docs.google.com/document/d/1ZIo0y746UsSRZIgRuuxwAbZjSBHitO_EanvwLYc-kGA/edit?tab=t.0I assume the gun was proved with 2 1/2" chambers, and the chambers have not been lengthened. The next time you tackle this ordeal, it is important to document the forward end of the chamber wall thickness also.
IMHO those numbers appear original and .027" left and .030" right at (about) 17 inches are not a concern, with shells generating pressures for which the gun was proved. The 9" numbers are a bit greater than are typically found on small bore game guns.
Under the 1896 Rules of Proof the 16 bore service charge was 1 oz. 2 3/4 Dram Eq. (1220 fps)
Pressures reported for bulk smokeless powder were “Schultze” - 8,250 psi & “E.C.” - 8,960 psi - both
+ 10-14% for modern transducer numbers.
