The HK416 uses a proprietary gas system derived from the HK G36, replacing the direct impingement gas system used by the standard M16/M4. 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. The
SA80 bull-pup assault rifle used this system long before the
HK G36 was developed. 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 HK416.".<sup id="cite_ref-1" class="reference">
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The HK416 is equipped with a proprietary accessory rail forearm with
MIL-STD-1913 rails on all four sides. This allows most current accessories, used on M4/M16-type weapons, to be fitted to the HK416. The HK416 rail forearm can be installed and removed without tools by using the bolt locking lug as the screwdriver. The rail forearm is 'free-floating' and does not contact the barrel, improving accuracy.
The HK416's barrel is
cold hammer-forged with a 20,000 round service life and features a 6 grooves 178 mm (7 in) right hand
twist. The cold hammer-forging process provides a stronger barrel for greater safety in case of an obstructed bore or for extended firing sessions. This includes "OTB" (Over-the-beach) capability; the HK416 can be safely fired after being submerged in water and not completely drained.<sup id="cite_ref-2" class="reference">
[3]