John Parker Lindsay patented a superposed, 2-shot muzzleloading rifle action in 1860, and remarkably, was able to get a contract to sell them to the US Federal Army. The system was fairly simple, with two percussion caps and firehouse leading to a front and rear chamber. The rifle was loaded with two successive charges of 60 grains of black powder and 500 grain bullets, and a single trigger fired the two rounds in succession.
In August 1863 the rifle was tested at West Point by Captain S.V. Benet and found acceptable. In fact, Benet found that the pressure from firing the first round tended to very firmly seat the second round, which then cleared fouling from the bore better than a regular rifle when it was fired. A contract was signed in December of 1863 for Army purchase of 1,000 Lindsay rifles at $25 each, and they were delivered in August of 1864. The rifles were issued to the 16th Michigan Volunteer Infantry, and saw use in the Battle of Peeble’s Farm.
Both in battle and in extended testing, the rifles were found to be flawed in ways they had not been initially recognized. Troops complained of double shots, with a single trigger pull firing both charges. Testing also found that the front chamber fire tube tended to foul and plug too easily, rendering the front chamber impossible to fire. No additional Lindsay rifles were purchased by the military. Lindsay did also make several versions of handgun using his system – these sold better than the rifles, but were still not a commercial success by most standards.