Daryl: Many thanks for checking. Heurteloup's French patent that year (a really lengthy one) seems to suggest forward-sliding barrels, but the drawings show the typical break-open design, so perhaps we're talking about different guns here.
By the way, the French patents of the 1830s and '40s show some remarkably advanced breechloading doubles, almost all of them of the break-open variety. For example, an 1847 patent by Pierre Loron shows a break-open double which is apparently striker fired, and opened by a simple push on a rearward extension of the trigger guard. Slick stuff!
