The 5.6×44mm XM144 was an experimental military small arms cartridge developed by Frankford Arsenal.
It was developed as a competitor to the AAI-designed XM110 round, but also fires a single, saboted flechette, the same type as used in the XM110. However, the XM144 uses a traditional-style casing of a different size.
There were different variations of this round. One of them is the original XM144 with the saboted flechette projectile, which is fired at a muzzle velocity of 1220 m/s. Another is the XM144WE4, which is designed to use traditional blunt projectiles. But, what makes the WE4 version different is that the casing was made slightly thicker to accommodate additional propellant. Because of the differences in the casing, neither version is universal.