Note the gauge number over C enclosed in the diamond mark was replaced in June 1924 with a long stylized C with gauge & chamber length in side as C12-65 with the C top & bottom gining out to the end of chamber length. This gun would thus be a pre 1924 gun. Many of the early inspector marks are unavailable & often later inspectors had the same initials.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra