The Spencer repeating rifle had a "rolling block" design. It was activated by lowering the trigger guard which opened the breech and extracted the spent cartridge shell. Raising the lever loaded a new cartridge from a spring-loaded 7-round magazine in the stock. The gun had few parts, many of which were common to the Sharps rifle. This made it easy and relatively inexpensive to make. One of its main advantages was its breech loading design. The Spencer proved to be very reliable under battlefield conditions. The muzzleloading rifles were slow to load compared to the Spencer. Also, in battlefield conditions, muzzleloaders could only aim the first few shots. With the enemy bearing down on them the remaining shots were fired as quickly as possible and were almost always poorly aimed. Muzzleloaders could fire only two or three shots a minute. A soldier trained to use the Spencer could fire from 20 to 30 aimed shots a minute when using a cartridge box that held 10 pre-loaded magazines. The only weakness of the Spencer was the small powder charge that did not have great range. But it proved to be an excellent rifle for the cavalry because they usually fought at close range. It allowed a smaller cavalry unit to lay down devastating firepower on an enemy. Several times, larger Confederate units had to retreat to save themselves from being cut to pieces by Spencer-equipped Union cavalry units.