Explanation: In the US Civil War, the Union had a much larger number of repeaters - guns which could fire multiple times before reloading - than the slaver scum in the South. Most guns at this time would have to be loaded with bullet, powder, and priming cap before firing a second time - a distinct delay before taking a second shot. Repeaters could fire five, six, seven times, or even more depending on the magazine size! This sounds unremarkable to us in the modern day, but it was a major innovation at the time.
The most famous was the Henry Rifle - complained by one Confederate officer to be a damn Yankee gun which could be loaded once on Sunday and fired all week!