The World Famous United States Automatic Rifle M4 Carbine 

The World Famous United States Automatic Rifle M4 Carbine
The M4 carbine, or M4 Carbine, is a shortened and lightweight version of the M16 assault rifle. The M4 carbine has 80% of the same parts as the M16A2. The M4 has semi-automatic and three-round burst firing options (same as the M16A2), while the M4 has semi-automatic and automatic options. The M4 was also sometimes equipped with a heavier barrel, to withstand the heat generated from automatic firing for long periods.
The M4 Carbine rifle is the choice of special forces and anti-terrorist forces, due to its size and full-automatic firing capability. These features are very useful for urban combat. Although the M4A1 does not have as long a shooting range as the M16 rifle, many military observers argue that shooting targets above 300 meters without a special rifle is unnecessary. The M4 is very effective at a distance of 150 meters.