|This article needs additional citations for verification. (January 2013)|
|Place of origin||USA|
|Bullet diameter||.550 in (Script error mm)|
|Neck diameter||.560 in (Script error mm)|
|Shoulder diameter||.560 in (Script error mm)|
|Base diameter||.560 in (Script error mm)|
|Rim diameter||.645 in (Script error mm)|
|Case length||.875 in (Script error mm)|
|Overall length||1.545 in (Script error mm)|
|350 gr (Script error g)||1,200 ft/s (Script error m/s)||1,125 ft·lbf (Script error J)|
|Source(s): Barnes & Amber|
Designed for the Spencer rifle and carbine, patented 6 March 1860, it was employed by cavalry during the American Civil War, first appearing at Sharpsburg in rifle form. No Spencer carbines were on issue at the Battle of Gettysburg, though two units under Custer had the rifles. The .56-56 was loaded with a slug of 350–360 gr (22.7–23.3 g) over 42–45 gr (2.7–2.9 g) of black powder. It was loaded by a variety of companies, and was also used in the Ballard and Joslyn carbines. It is a short-ranged cartridge, ineffective on anything larger than deer. Commercially loaded ammunition continued to be available into the 1920s.
The nomenclature of Spencer cartridges were unique. Unlike later cartridges like the .44-40 Winchester and .45-70, where the first number indicated caliber and the second the charge weight, the .56-56 refers solely to the case. The first 56 is the diameter of the case at the base .56 inches (14.2 mm), measured just past the rim, and the second 56 is the diameter at the case mouth, also 0.56 inches (Script error mm). Later versions of the cartridge included the .56-52, .56-50, and .56-46, which had varying degrees of taper in the cases, to accommodate smaller diameter bullets. All of these cartridges are rimfire primed. The actual bullet diameter of the .56-56 varied between .54 and .555 inches (13.7–14.1 mm), depending on ammunition manufacturer. The .56-52, made by Spencer, and the .56-50, made by Springfield, differed only in the degree of crimp, with the .56-50 having a greater crimp; both fired 350 grain .512-inch (Script error mm) bullets. The .56-46 fired a 320 to 330 grain .465-inch (Script error mm) bullet.