Short answers, pulled from the story.
The Agar gun was a hand-cranked machine gun developed during the American Civil War. It earned the nickname Coffee Mill Gun because its crank and ammunition hopper gave it a look similar to that of a common kitchen coffee grinder.
President Abraham Lincoln inspected the weapon at Washington Arsenal in 1861. He ordered ten weapons immediately at a cost of $1,300 each.
The rate of fire reached 120 rounds per minute to help prevent overheating. A metal jacket forced air through a turbine powered by the same hand crank used to fire the weapon.
In January 1862 the 28th Pennsylvania Volunteer Infantry used the Agar Guns in a skirmish by Harpers Ferry. Another engagement occurred at Middleburg, Virginia on the 29th of March 1862 when Captain Bartlett recalled Union soldiers firing an Agar Gun at attacking Confederate cavalry.
Ordnance Department officials condemned the design for using too much ammunition to be practical and because the single barrel proved prone to overheating while the weapon was also prone to jamming. In 1865, the few remaining Agar machine guns sold for $500 each.