The .450 Marlin is a firearms cartridge designed as a modernized equivalent to the .45-70 cartridge. It was designed by a joint team of Marlin and Hornady engineers headed by Hornady's Mitch Mittelstaedt, and was released in 2000, with cartridges manufactured by Hornady and rifles manufactured by Marlin, mainly the Model 1895M levergun. The Browning BLR is also now available in .450 Marlin chambering, as is the Ruger No. 1. Marlin ceased manufacture of the 1895M rifle in 2009. In October 2022 it was rumored that Ruger Firearms, the new owner of Marlin Firearms, may be reintroducing the 450 Marlin in their Model 1895 guide gun, but this has not been confirmed by Marlin or Ruger.

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".