During the Civil War, the Union purchased about 12,000 Spencer rifles and many tens of thousands of carbines, and the weapon became a standard arm for the Cavalry service. After the war, thousands of Spencers were in warehouses and arsenals in need of refit either from combat damage or just abuse and neglect. Springfield Armory took on the job of repairing these weapons after the war. In February of 1871, the Armory commandant suggested that he had received a batch of about 1,100 Spencer carbines from Fort Leavenworth, and that he could refit them into infantry rifles. This plan was approved by the Ordnance Department, and a total of 1,109 conversions were produced in 1871.
The conversion work was done by replacing the Spencer barrel with a new three-groove 1868 model rifle barrel (32.5 inches long) and 26 inch cleaning rod. Two barrel bands were used instead of the three on factory-original Spencer rifles. The wood and metal were refinished or repaired as necessary, and the receiver serial number (which could be anything from 1 to 34,000) was added to the left side of the barrel. If the carbine did not have a Stabler cutoff, one was added.