One doesn’t have to look very far to find reports about reliability issues in the 14.5-inch M-4 or other short-barreled carbines. It has reached the point that there is even a congressional inquiry into the reliability of the M-4 Carbine and the sole-source contract with its manufacturer. These issues stem from the fact that the M-4 platform is derived from the 20-inch M-16 series of rifles and, as such, compromises were made to reconfigure the nearly 50-year-old Stoner operating system to fit in a more compact package.
The most obvious compromise, and the biggest detriment to its reliability, is the shortened barrel and operating system. As the barrel gets shorter and shorter the gas port from which the weapon draws its operating power has to get larger and larger to provide sufficient back-pressure to function properly. As this gas port is enlarged, the amount of searing hot gases that operate the weapon is increased. Out of a shortened gas system these hot gases contain a much higher percentage of powder residue that is subsequently dumped right into the heart of the weapon. These hot gases also act as a literal degreaser that cooks off or otherwise blows out the lubrication that allows for reliable operation.