From what Ted Schefelbein has said in the past (I didn't request documentation or an affidavit), your extrapolation of DOM from chamber lgth is likely correct give or take a decade and probably made by Fusil Darne rather than the defunct Charlin. The "beach" photo of the fat lady's heel and toe doesn't really show the sliding breech or toggle lever very well and was taken only to call attention to the "recurve" in the comb.

jack