Necked-down Spencer family rimfire cartridge developed for improved velocity in post-Civil War Spencer sporting and military conversion rifles.
Type: Rimfire
Introduced: 1866, United States
Parent case: Spencer rimfire family
Standardization: Proprietary
Bullet diameter: 0.455" (11.56 mm)
Rim type: Rimmed
Primer: Rimfire
Production status: Discontinued
Also known as: .56-46 Spencer RF · .56-46 Spencer Rimfire
History: The .56-46 Spencer was developed after the Civil War as an improved loading for the Spencer repeating rifle, using a necked case to achieve higher velocity than the straight-walled .56-56 Spencer. It was used in later Spencer production and conversion rifles through the late 1860s before lever-action centerfire arms supplanted rimfire Spencers.