Le Redoutable: A Double-Barrel 20-Shot Revolver
11m
"Manufrance" was the common abbreviated name for Manufacture d'Armes et Cycles de Saint Etienne, a massive mail-order catalog company in France for many decades. Like Sears Roebuck in the United States, one could get pretty much anything from the Manufrance, including firearms. In the years leading up to World War One, the catalog included more and more extravagant revolvers, culminating in the 20-shot, 6.35mm "Le Redoubtable" (introduced in either 1910 or 1911) and the similarly-sized 16-shot "Le Terrible" in 7.65mm. Both used a cylinder with two staggered rows of chambers and two superposed barrels to fit that many cartridges into a sort of practical cylinder.
After 1914, the Manufrance catalog ceased publication for the duration of World War One, and the Redoubtable was no available when it returned in 1920. Before the war, this was definitely a luxury sort of item, bringing a price equal to that of a top-end self-loading pistol like a Luger, C96 Mauser, or 1903 Colt. A standard Army pattern Mle 1892 was less than half as much, and a pocket cyclists' Velodog sort of revolver was about a third the cost of Le Redoutable.