G.T. Garwood (Gough Thomas) Shooting Facts and Fancies, Chapter 34, 1978
Gives an average of .114” for end-of-chamber wall thickness for mid-20th century English 12g guns, but observes that higher tensile strength steel allows for lower wall thickness.

Jack Rowe demonstrates use of a vertical gauge starting at 2 minutes.
He states his lower limit is .020”, but clearly in reference to the distal 1/3 of barrel and he never addresses end-of-chamber wall thickness.


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