| 20/577 Alexander Henry | |
| Origin: | Scotland |
| Type: | Rifle |
| Designer: | Alexander Henry |
| Design Date: | 1895 |
| Production Date: | 1895 |
| Parent: | 20 bore |
| Case Type: | Rimmed, bottleneck |
| Bullet: | .584 |
| Neck: | .607 |
| Shoulder: | .674 |
| Base: | .706 |
| Rim Dia: | .754 |
| Rim Thick: | .06 |
| Case Length: | 2.75 |
| Length: | 3.27 |
| Bw1: | 560 |
| Vel1: | UNK |
| En1: | UNK |
| Bw2: | 570 |
| Vel2: | 1725 |
| En2: | 3770 |
| Balsrc: | The big game express &<br/>The Spanish Association of Cartridge Collectors |
The 20/577 Alexander Henry, also known as 20/577 Express, is an obsolete rifle cartridge.
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 calibre bullet like the .577 Black Powder Express.
The 20/577 Alexander Henry fired a lead, paper patched bullet driven by 6 drams (10.6 g) of blackpowder at, 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.