I'm probably wrong, but it never kept me from embarrassing myself
"Choke" indicates muzzle constriction > .008"
The chamber length (2 1/2"), shot charge (1 1/8 oz.) and 12 over C in the diamond are 1925-1954.
1925 - 1954 the 2 1/2” & 2 5/8” 12g maximum service load was reduced to 3 Dr. Eq. with 1 1/8 oz. shot with a mean pressure of 3 1/4 tons by LUP = 9,800 psi by Burrard’s conversion.
'3 tons per sq. inch maximum' and 12 in a diamond indicate 1954-1989.
As Miller said, under the 1954 Rules of Proof “Highest Mean Service Pressure” equivalent transducer values as converted from LUP by Burrard’s formula: 3 tons = 8,960 psi = 618 BAR
The original R bore (13) was .710"-.718" and when reproved was .729"
The original L bore (14/1) was .701" - .709", and when reproved was .719"
