The .45-70, also known as the .45-70 Government, .45-70 Springfield, and .45-21⁄10" Sharps, is a .45 caliber rifle cartridge originally holding 70 grains of black powder that was developed at the U.S. Army's Springfield Armory for use in the Springfield Model 1873. It was a replacement for the stop-gap .50-70 Government cartridge, which had been adopted in 1866, one year after the end of the American Civil War, and is known by collectors as the "Trapdoor Springfield".

The Springfield Model 1873 was the first standard-issue breech-loading rifle adopted by the United States Army. The rifle, in both full-length and carbine versions, was widely used in subsequent battles against Native Americans.