The 1862 version of the Gatling gun had reloadable steel chambers and used percussion caps. It was prone to occasional jamming. The Gatling gun saw only limited use in the American Civil War, but the conflict tested this weapon, perhaps the first successful machine gun used in warfare. Gatling used the six barrels to partially cool the gun during firing. Since the gun was capable of firing 600 rounds a minute, each barrel fired 100 rounds per minute. The gun had a number of problems, however. The bores were tapered, and often the barrels and chambers did not exactly align, affecting accuracy and velocity. The chamber system itself, in which a paper cartridge was contained inside a capped steel chamber, was both expensive and fragile. While the gun showed much promise and fired the standard .58-caliber ammunition, it had so many drawbacks and was so radical in design and purpose that Gatling was unable to interest the U.S. government. The army purchased none of his guns, but Maj. Gen. Benjamin F. Butler, after a field test, purchased 12 for $1,000 each. They were used on the Petersburg front in 1864 and were apparently considered successful. That, however, was the only active service the guns saw.
In January 1865 Gatling's improved model 1865 gun was tested by the Ordnance Department. Among other things, this weapon used rim fire copper-cased cartridges instead of the steel-chambered paper variety. Though this model did not see service, it was adopted officially in 1866. Having at least received government approval, Gatling began to sell his guns throughout the world; they achieved lasting fame in the post-war years. New models were produced regularly steadily improving the basic design up until the early 20th century. With the advent of the automatic machine gun, the U.S. Army declared their Gatling guns obsolete in 1911, after 45 years of service to the U.S. Army.