WOW Geno. I believe that is SIX IRON (acid etched) Crolle' and by far the earliest I've seen. Would the gun date to c. 1860-1870? Six Iron 'Turkish' did not appear on US guns until the Parker hammerless A grades.
DuPont was a common Walloon name, but I have no listing for a 'JJ' barrel maker- maybe Jean-Baptiste Delcour-Dupont's grand daddy?