A kick ass quality rifle chambered in 5.56x45 Nato rounds, same rounds used in the M16A2 (which is more accurate and has better control)and the M249 (inaccurate compared to the M16 and M4A1 but accurate enough for covering fire). But although to due the slight disadvantages from the M16 it has auto fire feature, it is ultra-upgradeable and its compact, and the model of the weapon is just superb.

The M4 Carbine is a shorter and lighter version of the M16A2 assault rifle, achieving 80% parts commonality with the M16A2. As with many carbines, it was meant to provide troops with an effective, shoulder-fired weapon in lieu of pistols, such as the M9. Since the weapon is shorter (and therefore lighter), it is handy and more convenient to carry than a full-length rifle. While this makes it a candidate for non-infantry troops (vehicle crews, clerks and staff officers) it has been used by US Special Operations Command (SOCOM) and others seeking a compact weapon for close quarters combat.

The M4A1 was developed and is produced for the United States government by Colt Firearms, who has an exclusive contract to produce the M4 family of weapons through 2009.

The M4A1 carbine, an improvement upon the M4 carbine intended for Special Operations use, features a fully-automatic fire mode, a flattop NATO M1913-specification rail on top of the receiver (for attachment of optics and other devices), and a detachable rail-mounted carrying handle. The M4A1 can be found in use in many US military units, including the U.S. Army Rangers, the elite Delta Force, U.S. Navy SEALs, and the United States Marine Corps Force Reconnaissance companies. Variants of the carbine built by different manufacturers are also in service with many other foreign special forces unit, most notably UK's SAS and Australia's SASR.

The M4A1 Carbine is specially favored by counter-terrorist and special forces...

Colt M4A1 Carbine
5.56x45mm NATO

The carbinized version of the venerable M16 series. The M4 carbine is used mostly by US special forces, but it is even used by the Israeli military. It is said that the M4 carbine will replace the M16A2/M16A4 assault rifle as the mainstay for the Us armed forces...
...but in MY opinion, I think the M16 should stay. The M4 is a great weapon and is battle-proven, but the M16 has a few advantages still over the M4. Although the M4 is full-auto (the M16 only fires 3-round bursts for its full-auto mode), very compact, and heavily upgradable, the M16 has power and accuracy. The M4, on the other hand, excels in other areas over the M16, but it's not as accurate or powerful as the M16.

The idea of the M4 replacing the M16 should be heavily under debate. For now though, the M4 is a favored carbine for our special forces.

Compact Weapon of the M16A2. This gun is widely used in most Special Forces (Especially NAVY SEALs) for its wide variety of customization such as the M203A1.

For those who play Counter Strike:

M4A1 5.56 mm Assault Rifle is a standard for Counter Terrorists (CT's) because of its short barrel length, rate of fire, and the ability to place a silencer when you right click your mouse. Though not that accurate especially in silent mode, it gives the CT a fighting chance against the Terrorist's feared weapons such as the AK47 and the Ingram MAC-10. With the Ingram being a fast firing low accuracy SMG (sub-machine gun) and the AK47, a long but powerful assault rifle, the direct rival of the M4A1.

Its accuracy is nothing when compared to the Steyr AUG but the AUG is loud and long, not good when entering CQB (closed quarters battle) operations and maps such as CS_Office. The M4 , as called by players, is chosen especially when you encounter low money, CQB maps, and if you don't have a weapon to choose from.

In silence mode, an enemy can not hear your shots as long as you are not near or beside the enemy. Its favored also since it can reach out even to a person carrying a Magnum Sniper Rifle, though it will take more than one shot to take out the sniper at long range unless your luck enough to...

A firearm derived from the M16A2/A4, commonly thought to be an extremely reliable and "1337" weapon. In actuality, the M4A1 (and M16 line, for that matter) requires constant cleaning and maintenance, and is extremely susceptible to jamming from sand and dust. Careful maintenance, however, can negate these negative effects.

It should also be noted that the M16/M4 fires the 5.56x45mm NATO cartridge, a bullet designed to WOUND, not KILL a target. The 5.56mm's lack of stopping power is proving problematic when faced with less squad-oriented enemies (this was noticed particularly in the 1993 conflict in Somalia and today in the Middle East). The 5.56mm was designed to basically incapacitate three men with one shot-- the wounded soldier, the medic that's supposed to work on him, and the soldier's friend/medic's assistant. Now, however, UN and NATO forces are facing insurgents that don't actually field treat dead or wounded.

The best mofo weapon on this globe, will shove up any punks ass and blow up any mofo cars that come pass buy if you implement the m203 grenade launcher, used by spec ops, it beats any AK in the world, M4A1 FOR LIFE BABA