Nitro Express

The Nitro Express (NE) series of cartridges are used in large-bore hunting rifles, also known as elephant guns or express rifles, but later came to include smaller bore high velocity (for the time) British cartridges.

The term "Express" was coined by James Purdey the younger in 1856, derived from the express train, to publicise the bullet velocity of his double rifles and became common parlance for many rifle cartridges. The addition of the word “Nitro” stemmed from the propellant used in these cartidges, cordite, which is composed of nitrocellulose and nitroglycerine.

The unveiling of the .450 Nitro Express by John Rigby & Company in 1898 heralded the beginning of the modern big game cartridge. Created from loading the already popular .450 Black Powder Express with cordite, the .450 NE was a fast and accurate cartridge capable of taking all African and Indian dangerous game.

Early extraction problems with the .450 NE was the catalyst for Holland & Holland to develop the .500/450 Nitro Express and Eley Brothers the .450 No 2 Nitro Express both with very similar ballistics and performance to the original. Rigby soon solved the problems with the .450 NE which quickly became the standard big-game cartridge used throughout Britain’s African colonies and India.

With the success of the .450 NE, various people (it is not clear who) decided to follow Rigby’s example and load the old .450/400 Black Powder Express, .500 Black Powder Express and .577 Black Powder Express cartridges with cordite, creating the .450/400 Nitro Express, .500 Nitro Express and .577 Nitro Express, the latter two offering greater power than the .450s at the expense of greater rifle weight and recoil. In 1903 Jeffery & Co decided to outdo them all, creating the .600 Nitro Express, the most powerful sporting cartridge commercially available for over half a century.

...
Wikipedia