The Rifle
Rifles gained popularity through the Civil War. Many used muskets during the war, but the practice of rifling increased the maximum distance a bullet could go. in this process, you would bore holes in the barrel of your musket, which would then allow bullets to go further.
Spencer Repeating Rifle
The repeating rifle was a weapon that was very powerful for its time. Compared to muskets, which could only shoot 2 to 3 rounds per minute, the repeating rifle could shoot up to 20 rounds per minute. The War Department foresaw a logistics problem with the rifles, they predicted that a rifle which shot so fast would consume the ammunition supplies of the US too quickly.
Because of this logistics problem, the War Department declined to provide a government contract for the rifles at first.