The Allen and Wheelock lipfire revolver,
Invented by Ethan Allen in 1860, the Allen and Wheelock revolver was an attempt to circumvent the Rollin White patient on the bored through cylinder, which allowed for practical metallic cartridge revolvers, and the rimfire cartridge held by Smith and Wesson. The new revolver used metallic cartridges called “lipfire cartridges” which featured a small lip containing mercury of fulminate which served as the priming component of the cartridge.
Ethan Allen claimed in his patent application for the lipfire cartridge that it was meant to reduced costs compared to the rimfire, where priming component rimmed the entire cartridge. The cartridges had to be placed lip up, and recessed were machined into the cylinder so that the lip would fit snugly. The Allen and Wheelock lipfire revolver came in both .36 caliber (Navy) and .44 caliber (Army) models.
While the revolver was intended to evade the Rollin White patent, the fact of the matter was that it still had a bored through cylinder. Only 500 were produced before Rollin White and Smith & Wesson filed court injunctions, forcing Allen and Wheelock to cease production in 1863.