A popular Civil War levergun, the Spencer was personally endorsed by President Abraham Lincoln after it was demonstrated to him.
Loaded by a magazine tube in the butt, the Spencer held 7 rounds. While the levergun has been referred to as the "56-56", the actual bore diameter was .52 caliber.
After the war the calibers were designated "56-52" and "56-50" and are these days noted as the .52 caliber and the .50 caliber.
The cartridges were of the rimfire type.
Over 250,000 rifles and carbines were sold the US government.