The M416 uses a proprietary gas system derived from the HK G36, replacing the direct impingement gas system used by the standard M16/M4.

The HK G36 gas system was in turn derived from the AR-18 assault rifle designed in 1963.

The HK system uses a short-stroke piston driving an operating rod to force the bolt carrier to the rear.

This design prevents combustion gases from entering the weapon's interior, a shortcoming with direct impingement systems.

The reduction in heat and fouling of the bolt carrier group increases the reliability of the weapon and extends the interval between stoppages.

It also reduces operator cleaning time and stress on critical components.

According to H&K "experience that Heckler & Koch gained during its highly successful 'midlife improvement programme' for the British Army SA80 assault rifle, have now borne fruit in the M416".

The M416 is equipped with a proprietary accessory rail forearm with MIL-STD-1913 rails on all four sides.