Revdocdrew/Dave;
I may be totally awash on this but it is my understanding from the various articles on proof that the chamber dimensions & bbl wt were only required to be stamped on guns bearing the "Voluntary" smokeless proof, prior to 1924. This gun was obviously proofed prior to 1924 & does not show the nitro proof mark. The marks would thus appear to be correct for the era.

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