M4 carbine

The M4 Carbine is a firearm tracing its lineage back to the earlier carbine versions of the M16, all based on the original AR-15 made by ArmaLite. It is a shorter and lighter version of the M16A2, with 80% parts commonality with the M16A2. The M4A1 has selective fire options including semi-automatic and full-auto. It fires the 5.56x45mm NATO round, and is suitable for C.Q.C. Although the M4 has less effective range than the longer M16, many military analysts consider engagement with a non-specialized small arm above a range of 300 meters (330 yd) to be unnecessary. It is effective at ranges of 150 meters (160 yd) or less and has a maximum effective range of about 500 to 600 meters (550–660 yd).

Battlefield 2
The M4 Carbine is the standard primary weapon for the USMC's Special Forces kit. It has a Aimpoint M2 Sight attached to it, enabling an un-obstructed field of view when aiming. The M4 Carbine has reasonably high accuracy but with a low damage output. However, the lack of stopping power is balanced out by the weapons rate of fire. This makes the weapon very effective for many situations. When compared to its MEC counterpart, the AKS-74u, it has better accuracy and a better sight, but has a lack of stopping power. When compared to its PLA counterpart, the QBZ-97, it has identical stats for damage output and accuracy, but the M4 is considered superior because of its Aimpoint M2 Sight, while the QBZ-97 has only iron sights.

Battlefield 2: Modern Combat
In Battlefield 2: Modern Combats singleplayer, the M4 Carbine' is issued to NATO assault-class soldiers during Radio Silence. It has a moderate rate of fire, a 30 round magazine, high damage and good accuracy. It can kill in a single head shot and is effective as a sharpshooting weapon with its ACOG-like scope. It also has an M203 attached to it, though it is originally unusable. Blind firing for head shots and the grenade launcher can easily dispose of a large amount of enemies.

In multiplayer, it is issued to the USMC Assault kit and can be used similarly to how it's used in singleplayer.

Battlefield Play4Free
In Battlefield Play4Free, the M4A1 is a buyable elite assault rifle for the Assault Kit. It features high damage and a 20-round magazine. However, the weapon suffers from a decreased range and a more moderate recoil, as well as a cost of up to 1249 for unlimited use. The weapon's extra magazine and decent damage make it excel at close-range infantry-based maps like Sharqi and Basra, but it's still efficient on longer range maps like Karkand.

Battlefield 3
In Battlefield 3, both the M4 and M4A1 are included as Engineer weapons. It was first seen in the Fault Line trailers with a Trijicon ACOG and a tactical flashlight. However, during the live console debut on Late Night with Jimmy Fallon, the M4's ACOG has been replaced with an EOTech, the tactical flashlight has been switched to the right set of R.I.S. rails, and the reload animation is completely different from the animation seen in the Fault Line trailers, as the player hits the bolt catch instead of pulling the charging handle.

M4A1
In multiplayer, the M4A1 is the default carbine for the United States Marine Corps Engineer kit. It is capable of fully-automatic or semi-automatic fire, has low recoil, making it very accurate at medium and short ranges. It can do a fairly high amount of damage due to its fast firing speed.

The weapon's main strength is its very high rate of fire which is one of the fastest of all carbines, but it is also one of it's weaknesses as the rate of fire is so fast that it's hard to actually fire the gun in controlled bursts, as it might make you accidentally fire an extra round or two which by then the recoil already kicked the weapon out of aim so lots of ammo may be wasted and lots of missed shots may be made.

The M4A1 and AKS-74u are the last Engineer unlocks for 145,000 points which allows the player to have the weapon from the other faction, allowing USMC Engineers to use the AKS-74u and Russian Ground Forces Engineers to use the M4A1.

M4
The M4 becomes available at 40,000 Engineer score. It has the same stats as the M4A1, but fires in either three-rounds burst or semi-automatic. After the recent patch, the M4 has more vertical recoil and less horizontal recoil than the M4A1. The M4 can be used by both factions and share its unlocks with the M4A1. This means that any unlocks obtained for the M4A1 will be available to use on the M4 and vice versa.

Trivia

 * In Battlefield 2, if a player uses the console command, the M4's Aimpoint M2 Sight disappears.
 * In the Pre-Alpha stages of Battlefield 3, as seen in the Fault Line trailers, the M4A1's appearance was that of Medal of Honor's M4A1 multiplayer model, which DICE helped develop.
 * The model of the M4 in Battlefield 2 has several issues. The lower reciever has printed on it "M16 A2" instead of M4, and the fire selector switch is set to "semi".
 * In Battlefield 3, The M4A1 has Magpul Ranger Plates on the bottom of it's STANAG Magazine.
 * In Battlefield 3, The M4A1 reload animation has slightly changed in full release.
 * There was a glitch that, once the M4A1 Russian Acquired version was unlocked, the AKS-74u and M4A1 would stay faction specific and the player would have to keep switching back and forth if they wanted to keep using one or the other. DICE has fixed this bug in the 1.04 patch.
 * Also, while using the M4A1 as a Russian, the meter below the ammo counter doesn't show how far you are from unlocking another attachment. This applies to all faction-specific weapons acquired by the other faction.
 * The M4A1 is actually painted with a tan camoflauge in the game. It is noticable in bright environments, but when there is shade, it looks like the blackish-grey color seen in almost every other picture of it.

Videos
Video:M4A1 BF2|Gameplay with the M4 in Battlefield 2 Video:Battlefield 2 - M4 Third Person reload animations|Third-person reload animation from the M4 in BF2 Video:Battlefield 3 - M4 Sound|Sound from the M4 in Battlefield 3