Around 1871, Springfield Armory converted 1,108 Burnside Rifle Co. Spencer carbines by fitting the actions with rifle length barrels chambered for .50 caliber ammunition (56-50 Spencer) with three groove rifling. The armory also refurbished the parts and added a nearly full length forearm with two barrel bands and a slotted cleaning rod. The left side of the stock, just behind the saddle ring base, is marked with the correct "ESA" cartouche, and the other components have the standard Burnside and armory markings. It has a blade front sight, notch and folding ladder rear sight, and the Stabler cut-off device.