One of the big gun companies, H&K I think, was asked to improve the M4. The main improvement was changing form the direct impingement gas system to a piston gas system.
H&K, huh?
Funny, the German Ministry of Defense has decided that the H&K 36, the standard Bundeswehr infantry rifle, is defective (lack of accuracy) caused by sensitivity to environmental heating and the use of different plastics in the receiver.
“The main improvement was changing form the direct impingement gas system to a piston gas system.”
And increased weight noticeably. It is no more or less reliable than the original.