The .577 Tyrannosaur or .577 T-rex is a proprietary cartridge developed by A-Square in 1993. It is an entirely new design, not based on any previous cartridge for the hunting of large game in Africa. The .577 contains a .585 inch diameter 750-grain (49 g) Monolithic Solid Projectile which when fired moves at 2,460 ft/s (750 m/s) producing 10,180 foot-pounds force (13,800 J) of energy. For comparison the .223 Remington/NATO 5.56mm round used in weapons such as the M16 rifle, when using a 77-grain (5.0 g) projectile, moves at 2,750 ft/s (840 m/s) producing 1,293 foot-pounds force (1,753 J). The production model from A-square is based on their Hannibal rifle platform, which also comes in other large rifle calibers as well.
There has been an increased amount of interest in this cartridge due to its exposure in the many online video sites. The many videos are generally titled "massive recoil" and show many people firing a rifle in this caliber being thrown backwards and falling over due to the recoil produced. These videos have been criticized as featuring people uneducated in shooting large caliber rifles. At the end of one of the most popular videos, a man shoots a large rifle with no ill effects.[However, this rifle is misidentified and is not a .577 Tyrannosaur model, but rather a .700 Nitro Express built on a single-shot .50BMG action by the members of www.accuratereloading.com.
Many websites have done reviews of the .577 Tyrannosaur, with the general consensus being that it is impractical. One stated reason being the fact that on an animal of large size shot placement is more important than the size of the bullet. Another reason being that the amount of recoil produced with full power loads only allows for a single shot in an environment requiring a possible second shot in quick succession. However, when the ballistics are reduced to the range of .577 Nitro Express levels, recoil and recovering time are much more manageable. A-square does not specifically take a stand on this issue, but seem to imply a focus on hunting, especially African big game hunting. There is a story that it was created for sheer knockdown power of charging big game animals, but it is unclear if this is true.