The fault with the M-4 is mostly carbon build-up in the gas-powered receiver assemblies - the propellant burn causes the piston to jam.
A modification of the gas-powered system, the HK-416, has apparently solved this problem in the field, but it is not standard military issue.
According to the solicitation for the new upper receiver assemblies, the 416 “allows Soldiers to replace the existing M4 upper receiver with an HK proprietary gas system that does not introduce propellant gases and the associated carbon fouling back into the weapon’s interior. This reduces operator cleaning time, and increases the reliability of the M4 Carbine, particularly in an environment in which sand and dust are prevalent.”
One wonders at the priorities of the military procurement system.
Carbon build up was a problem in the M-16 back in RVN! 40 years and no progress?
There is nothing about a piston rifle design that makes it immune to sand, which according to the article is the primary cause of failure.
What piston? There is no piston in a M4.