The nomenclature of Spencer cartridges was unique. Unlike later cartridges such as 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 . 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 bullets. The .56-46 fired a - bullet. The Spencer rifle used a
tubular magazine. To control the risk of accidental discharge owing to recoil, Lugs describes the .50 calibre round as having been reduced in calibre in order to minimise this. ==See also==