At first, 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 carbine breechloaders that loaded one shot at at time. Such carbines were shorter than a rifle and well suited for cavalry.) More accurately, they feared that the armies 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. A weapon able to fire several times as fast would require a vastly expanded logistics train and place great strain on the already overburdened railroads and tens of thousands of more mules, wagons, and wagon train guard detachments. The fact that several Springfield rifle-muskets could be purchased for the cost of a single Spencer carbine also influenced thinking.
However, the Spencer repeating carbine was eventually adopted by the Union cavalry and saw service during the American Civil War.
This exceptionally nice Spencer carbine that was manufactured by the Spencer Repeating Rifle Company, Boston, Massachusetts during the Civil War and arsenal rebuilt for the Indian Wars. The top of the receiver is marked "SPENCER REPEATING/RIFLE CO. BOSTON, MASS./PAT'D MARCH 6, 1860"
This particular Spencer carbine is equipped with the Stabler cut-off.
In the latter part of the war Edward M. Stabler of Maryland invented the Stabler Cut-Off Device. It prevented the cartridge from feeding the magazine to the receiver by limiting the lowering of the breech block. (the small lever just forward of the trigger) The carbine could then be used as a single shot weapon.