As pertains to bore size I believe a gun is considered "In Proof" if it has not been enlarged more than .008" (.2mm) over proofed diameter. I can tentatively make out .729" for the right bbl, but can't see the left bbl size. This would mean that as relates to bore size only at least the right bbl would still be in proof for the loads which meet proof specs ie, 3 tons. It would not be proofed for US SAAMI spec loads of course. With the decimal dia & tons pressure this appears to me to be a post 1954 proof.
