556x49mm

556x49mm is a type of ammunition used primarily in firearms, particularly in the United States. It is a rimless, bottlenecked cartridge designed to be fired from the M16 rifle and its variants, as well as other firearms chambered for this caliber. The 556x49mm cartridge is known for its reliability, accuracy, and versatility, making it a popular choice for military, law enforcement, and civilian use.

The cartridge features a 5.56mm (0.22-inch) diameter bullet and a 49mm (1.93-inch) overall length. It is typically loaded with a 55-grain (3.6-gram) full metal jacket (FMJ) bullet, although other types of ammunition, such as hollow-point and armor-piercing, are also available. The 556x49mm cartridge is propelled by a powder charge that provides a muzzle velocity of approximately 915 meters per second (2,999 feet per second) and an effective range of around 550 meters (600 yards).

The 556x49mm cartridge was developed in the 1950s as part of the Armalite AR-15 rifle project, which aimed to create a lightweight, reliable, and accurate rifle for military and law enforcement use. The cartridge has since become one of the most widely used and recognized cartridges in the world, with millions of rounds produced annually. Its popularity is due in part to its compatibility with a wide range of firearms and accessories, as well as its relatively low cost compared to other high-caliber cartridges.