I have the same carbine. The Confederates joked it the gun that was "loaded on Monday and fired all week." In 1863, Lincoln took a direct hand in getting the carbine approved through the typical conservative military bureaucracy, and Federal cavalry units (among them Custer's) used it with great success for the remainder of the war.
The Spencer was also very reliable for the period and could maintain a rate of fire of 20 rounds a minute compared to 2-3 rounds for the muzzle loading Springfield or Enfield. It also essentially had waterproof ammunition which was another huge advantage over the paper cartridges used in the rifled muskets of regular infantry. It used a tubular magazine that loaded through the butt just like a modern Browning .22 (not much truly new in firearms' design that those fellows hadn't solved a long time ago).
After the war , the cavalry was forced to take a step back and adopt the carbine length, single shot trapdoor carbine. However the Spencer soldiered on in the hands of settlers headed west and in the hands of indigenous tribes who employed quite a few against the trapdoor armed cavalry at places like Little Big Horn. You can see one in use in Eastwood's great movie "Unforgiven."
Spencer with magazine removed.
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There were a number of other successful cavalry carbines as well. One of the better ones was the Joslyn. It was single shot, employing a rotating chamber closing mechanism. The designer cleverly decided to chamber it in the Spencer cartridge.
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But the best was the Spencer. And yes, one in good shape with some casecolor left on the action, can be pretty expensive.