The .450/400 Black Powder Express cartridges were black powder rifle cartridges introduced in the United Kingdom in the 1880s.

The .450/400 Black Powder Express cartridges are bottlenecked centerfire black powder express rifle cartridges produced in two case lengths, 23⁄8 inches (60.3 mm) and 31⁄4 inches (83 mm). Both cartridges were later loaded as "Nitro for Black" cartridges, the same cartridges loaded with mild loadings of cordite carefully balanced through trial to replicate the ballistics of the black powder versions.^[1]

The .450/400 23⁄8 inch Black Powder Express was loaded with a bullets from 210 to 270 grains (14 to 17 g) driven by 79 to 84 grains (5.1 to 5.4 g) of black powder. The .450/400 23⁄8 inch Nitro for Black was loaded with a jacketed 270 grain round nose bullet driven by 38 grains (2.5 g) of cordite.^[1]

The .450/400 31⁄4 inch Black Powder Express was loaded with a bullets from 230 to 300 grains (15 to 19 g) driven by 110 grains (7.1 g) of black powder. The .450/400 31⁄4 inch Nitro for Black was loaded with bullets of 270 to 316 grains (17.5 to 20.5 g) driven by 45 to 48 grains (2.9 to 3.1 g) of cordite.^[1]

The .450/400 Black Powder Express cartridges served as the parent cases for the .450/400 Nitro Express cartridges, the same cartridge cases loaded with greater loads of cordite and heavier bullets to produce far more powerful rounds.^[1][2]

The .450/400 Black Powder Express in both cartridge lengths were developed in the 1880s by necking down the .450 Black Powder Express, the .450/400 23⁄8 inch Black Powder Express simply a shortened version. The .450/400 31⁄4 inch Black Powder Express was listed in the Kynoch catalogue of 1884 as the .450 reduced to . 400.^[1]

Whilst obsolete, .450/400 31⁄4 inch Black Powder Express ammunition can still be purchased from ammunition manufacturers such as Kynoch.^[2]

The .450/400 Black Powder Express in both case lengths were considered good deerstalking cartridges and was usually chambered in a lightweight stalking rifle.^[1]

• Express (weaponry)
• List of rifle cartridges
• List of rimmed cartridges
• 10 mm caliber

• Ammo-One, ".450/400 B.P.E. 31⁄4 inch", ammo-one.com Archived 2020-11-06 at the Wayback Machine, retrieved 8 November 2017.
• Cartridgecollector, .450/400 2 3⁄8" Black Powder Express, cartridgecollector.net, retrieved 17 Dec 16.
• Cartridgecollector, .450/400 2 3⁄8" Nitro for Black Powder, cartridgecollector.net, retrieved 17 Dec 16.
• Cartridgecollector, .450/400 3 1⁄4" Black Powder Express, cartridgecollector.net, retrieved 17 Dec 16.
• Cartridgecollector, .450/400 3 1⁄4" Nitro for Black Powder, cartridgecollector.net, retrieved 17 Dec 16.
• The Spanish Association of Cartridge Collectors, ".450-400 Express 23⁄8 inch", municon.org Archived 2017-11-01 at the Wayback Machine, retrieved 8 November 2017.