This 12ga was black powder proofed between 1893-1924. It seems to have been resubmitted for nitro proof since 1959.
Pete; What are you basing this on. It appears to have been originally Nitro Proofed to me. The chamber dia (20.6) is normally found only on guns receiving the Nitro Proof & was discontinued in 1924 with the new chamber marking. Lion over PV seems to have been introduced for military rarms in 1898 & for all arms after 1903. This would thus seem to me to be a gun which was built & smokeless powder proofed between 1903-1924.
PS; Double check that 10.3, bet its an 18.3 (.720") for bore with a choke dia of 17.3 (.681) which would be a Full @ .039" (1mm) constriction.
