AR's
The HK416 (5.56 mm) was developed by Heckler & Koch for U.S. special operations forces as a major product improvement of M4/M16-type carbines and rifles. Using the HK-proprietary gas piston system found on the G36, the HK416 does not introduce propellant gases and carbon fouling back into the weapon’s interior, making it the most reliable of any M4/M16 type weapon. The HK416 has been combat-proven in Southwest Asia and has also gained the attention of military, law enforcement, and security users outside of the US. In April 2007, the HK416 was selected as the new Norwegian Army rifle.
Heckler & Koch - USA