The M4 carbine is the standard issue weapon of most US forces, based on the M16, shortened with a collapsible stock. The basic design employed by the M4 is over two decades old, with upgrades coming every-so-often to keep the weapon system up to date. It currently is on its second variant, the M4A1, which has mount rails along the top of the body and rails along all four sides of the fore grip that can be used to attach different sights, grips, and different kinds of accessories to assist soldiers wielding the M4. However the gun is not without its faults. It has a problem with jamming, especially in harsh conditions. In 2007, there was a dust test conducted by the US Army where they took the M4 and the XM8, HK416, and the FN SCAR. They took ten of each gun and had them fire 6,000 rounds per rifle. The results showed that the XM8, HK416, and FN SCAR all had fewer than 235 stoppages, while the M4 had 882 stoppages.
The HK416 is a completely new weapon system that just happens to look almost identical to the M4. It can take on all the accessories that the M4 currently uses, and the HK416 has improved the gas system to lead to fewer malfunctions, has an improved magazine and housing (a big reason for the high number of malfunctions in the M4), and has the ability to fire more rounds per barrel than most weapons suiting to replace the M4. The fact of the matter is, the HK416 is a drastic improvement over the aging M4, without needing a total new set of accessories, cleaning supplies and instructions, and ammunition.
