The LeMat revolver (sometimes referred to as the grapeshot revolver) is something of an anomaly. Patented by Dr. Francois Alexandre LeMat in 1856, it appears to be a simple revolver with a cylinder for loading nine bullets. There are varieties varying from .32 calibre to .42 calibre. The interesting thing about a LeMat revolver is that the pin about which the cylinder revolves is actually a large-calibre barrel (somewhere between .41 and .63 calibre) that fires a load of shot. It's sort of a revolver and a handheld shotgun combined into a single weapon. The hammer has an adjustable striker allowing the wielder of the gun to switch between firing one of the bullets through the upper barrel and firing the load of buckshot from the lower barrel.
They were first constructed in New Orleans in the 1860's, but then a little thing called the American Civil War happened. LeMat moved construction to France with the intention of selling the revolvers to the Confederate Army. The first batch was of such shoddy construction that construction was again moved, this time to Birmingham, England. The gun was a favorite personal handgun amongst a select few high-ranking Confederate officers.
There is considerable variation amongst LeMat two-barrel revolvers. There are .40 and .42 calibre varieties as well as a "Baby LeMat" which is a 9-shot .32 calibre gun with a .41 calibre buckshot barrel. The Baby LeMats are very rare; there were probably no more than 100 ever built. Also produced was the LeMat two-barrel revolving carbine which bears a resemblence to a rifle with two shortened barrels. The carbine had a nine-shot .42 calibre cylinder and a .63 calibre grapeshot barrel. It is unknown how many of the carbines were created.
LeMat continued to improve upon the designs of these weapons until his death in 1883, but the gun had gone out of style many years after the war had ended.