One of the deadliest guns of the Civil War, and perhaps of any war, was the Gatling gun. This weapon of destruction was invented by Richard J. Gatling during the Civil War, and was extremely useful due to it requiring a reload much less frequently. The gun was also very effective from long ranges, and could even be outfitted onto boats.
After being created by Richard J. Gatling, he sold to the Union, who bought just a few initially. However, Gatling was also a Confederate sympathizer, and was a part of a group called the American Knights, which supported Confederates. As a result, he also offered the South a chance to buy the product.
However, the product was never adopted by either the Union or Confederacy. The Union only purchased a few of the guns, and General Custer famously decided not to use them in the battle commonly called "Custer's Last Stand." This was mostly due to the inability to carry the gun around, making it hard to transport quickly. The gun was eventually phased out by the handheld machine gun.
The gun was manufactured in two different models, the .58 caliber and the .3 caliber. Both models shot insanely quickly for the time period, as the .58 could shoot 350 rounds a minute, and the .3 a whopping 400 rounds per minute.
The Gatling gun required hand cranking, and was on wheels so it could be moved short distances fairly quickly (although this wasn't enough; see above). It was very heavy, but could shoot for a while without a reload being necessary.
While the Gatling gun remains one of the most infamous Civil War weapons, there were many other incredible "machines of murder" which played a huge part in many battles. Many of their qualities can even be seen in guns today. Below you can find more examples of the devices used to achieve what would eventually be a Union victory.