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 Joslyncarbines. It is a short-ranged cartridge, ineffective on anything larger than deer. Commercially loaded ammunition continued to be available into the 1920s and 1930s.
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