20/577 Alexander Henry

The 20/577 Alexander Henry, also known as 20/577 Express, is an obsolete rifle cartridge.

Overview
The 20/577 Alexander Henry was developed and introduced by the Scottish gunmaker Alexander Henry around 1895 exclusively for his hunting rifles.

The 20/577 Alexander Henry is a rimmed, bottlenecked centerfire rifle cartridge. The 20/577 Alexander Henry is derived from brass 20 bore cartridges necked down to accept a .584 in calibre bullet like the .577 Black Powder Express.

The 20/577 Alexander Henry fired a 560 or lead, paper patched bullet driven by 6 drams (10.6 g) of blackpowder at 1725 ft/s, its ballistic performance replicating that of the .577 Black Powder Express 3-inch. Later versions were loaded with mild loadings of cordite, carefully balanced through trial to replicate the ballistics of the blackpowder version, a copper-tubed lead bullet was also available, offering improved performance against dangerous game.