The US army's rifle of choice has failed to perform against three newer carbines in recent extreme dust tests.
Colt Defence's M4 was tested alongside FNH USA's Special Operations Forces Combat Assault Rifle and Heckler & Koch's XM8 and HK416 rifles.
Officials tested ten of each of the four models, firing 6,000 rounds under sandstorm conditions.
The M4 recorded 882 stoppages, compared with the best performing rifle, the XM8, which recorded 127 stoppages.
The M4 uses a gas tube system which blows carbon residue into the firing mechanism, which can lead to fouling and heat that dries lubrication, causing excessive wear on parts.
The three other models use a piston-style system that uses a gas-driven piston rod to cycle the weapon during firing.
By staff writer