Once the breechblock is clear of the receiver, the carrier "rolls" downward, ejecting a spent cartridge from the chamber and collecting a fresh round from the tubular magazine in the buttstock.

When Spencer signed his new rifle up for adoption right after the American Civil War broke out, the view by the Department of War Ordnance Department was that soldiers would waste ammunition by firing too rapidly with repeating rifles, and thus denied a government contract for all such weapons.

(They did, however, encourage the use of breech-loading carbine, which is also single-shot like most firearms of the day, but is shorter than standard rifles and thus more suited to mounted warfare)[17] More accurately, they feared that the Army's logistics train would be unable to provide enough ammunition for the soldiers in the field, as they already had grave difficulty bringing up enough ammunition to sustain armies of tens of thousands of men over distances of hundreds of miles.

[18] However, shortly after the July 1863 Battle of Gettysburg, Spencer was able to gain an audience with President Abraham Lincoln, who invited him to a shooting match and demonstration of the weapon on the lawn of the White House.

Ripley disobeyed the order and continued to use the old single-shooters, causing him to be replaced as head of the Ordnance Department later that year.

Notable early instances of use included the Battle of Hoover's Gap (where Colonel John T. Wilder's "Lightning Brigade" of mounted infantry effectively demonstrated the firepower of repeaters), and the Gettysburg Campaign, where two regiments of the Michigan Brigade (under Brigadier General George Armstrong Custer) carried them at the Battle of Hanover and at East Cavalry Field.

At the Battle of Nashville, 9,000 mounted infantrymen armed with the Spencer, under the command of Maj. Gen. James H. Wilson, chief of cavalry for the Military Division of the Mississippi, rode around Gen.

President Lincoln's assassin John Wilkes Booth was armed with a Spencer carbine at the time he was captured and killed.

Compared to standard muzzle-loaders, with a rate of fire of 2–3 rounds per minute, this represented a significant tactical advantage.

[23] One of the advantages of the Spencer was that its ammunition was waterproof and hardy, and could stand the constant jostling of long storage on the march, such as Wilson's Raid.

[6] In 1867 Brigadier General James F. Rusling of the Quartermaster's Department recommended cavalry exclusively use the carbine against mounted Indian raiders, after completing a one-year tour of the new western territories.

"[29] In the summer of 1870–1871 Chilean cavalry adopted the rifles, a change that substantially increased military disparity with the indigenous Mapuche who were at war with Chile.