M4A1 Carbine

The M4 Carbine is a family of firearms tracing its lineage back to earlier carbine versions of the M16 rifle, all based on the original AR-15 made by ArmaLite. It is a shorter and lighter version of the M16 assault rifle, achieving 80% parts commonality with the M16A2. The original M4 carbine was based directly off the M16A2 assault rifle, including being three-round-burst instead of fully automatic (a feature found in its successor, the M4A1). Originally intended for support crews and special forces in need of a compact weapon, the M4A1 is now the de Facto American Urban warfare rifle. Nowadays, while the M4 is commonly associated with its original manufacturer Colt, hundreds of clones of AR-15 based rifles exist. Due to complaints about about the M4's insufficient stopping power as its carbine-length prevents it from having as much muzzle energy as the M16, as well as complaints on the overall M16 design such as constant maintenance and fouling, have prompted the US military to seek out replacements for the M4; weapons such as the SCAR and HK416 have been trialed for general issue, but a successor has not yet been found.

Singleplayer
In singleplayer, the M4A1 (with a Tasco Red Dot Sight, AN/PEQ-2A, and foregrip) is a frequently dropped weapon among the Marines, and an infrequently dropped weapon among the SAS troops. It is the starting weapon in Charlie Don't Surf and Game Over, and one of the optional weapons at the beginning of Hunted. The "M4A1 Grenadier", which uses an EOTech Holographic Weapon Sight, AN/PEQ-2A, and a M203, is the starting weapon in The Bog, War Pig and Shock and Awe. The "M4A1 SOPMOD" uses the Red Dot Sight, M203 grenade launcher, AN/PEQ-2A infrared laser, and silencer, and is the starting weapon in the majority of the British missions. Captain Price uses the M4 (either a suppressed M4A1 in silent missions or the Grenadier version) in all missions. Surprisingly, in the SAS missions, the M4A1 SOPMOD seems to have all attachments available, a red dot sight, silencer, grip, M203 grenade launcher. Though the M4A1 Carbine has a grip, this does not serve to decrease recoil and does not count as an attachment. Note that the grip does not show from the third-person perspective in-game, as when dropped or held by another character, in both single-player and multiplayer.

Multiplayer
In multiplayer, the M4A1 Carbine has an attached foregrip. It can be modified with the Red Dot Sight, ACOG Scope, M203, or silencer. The M4A1 Carbine is pretty good with moderate damage and very low recoil, but it has very high idle sway (4 degrees) and idles very fast, making it more difficult to aim with at long range. This was done for balancing purposes because the M4A1 was incredibly overpowered in the beta, in which it had no idle sway. The M4A1 also shares ammo with the M16A4 and the G36C. The M4A1 Carbine is one of the most commonly used weapons in online multiplayer on all platforms.

As stated above, the M4A1 is not particularly effective at long range due to its sway on consoles. In the PC version, however, idle sway is easily compensated for with the mouse, making it very effective at all ranges. The same goes for the Wii version; if you have a steady hand you can control the sway with the Wii remote, making the weapon devastating. The M4 is ideal in close quarters combat due to its high rate of fire. Steady Aim also makes the M4 a fairly effective hip-fire weapon. Double Tap can be quite effective due to low recoil and low damage, but ammo use increases dramatically. Another VERY good perk is stopping power for the rifle, which makes it deadly at all ranges.

The weapon's low damage output can be compensated by its high rate of fire, and the very low recoil allows for accurate full automatic fire at short and medium ranges. Because of this, Bandolier can be useful. For these reasons, a Suppressor or a Red Dot Sight is a good choice.

Singleplayer
The M4A1 returns in Call of Duty: Modern Warfare 2 and has retained most qualities and appearances of the Call of Duty 4 version. It has much less sway and slightly more recoil compared to the previous version. The AR-15 carry handle which was present in Call of Duty 4 has been replaced with foldable PRI front and ARMS #40L rear sights and the Knight's Armament Rail Interface System (RIS) has been replaced with an ARMS Selective Integrated Rail (SIR) System. It now sports tan camouflage, as opposed to the previous gunmetal color. The M4A1 retains the foregrip, although it is absent in the create-a-class profile image. The M4 comes in many variants in the single player campaign, such as the M4A1 SOPMOD and the M4 Grenadier w/ Holographic, usually featuring more than one attachment. The M4A1 is the weapon of choice for the US Army. The Rangers in-game and reality, use the M4A1 but they are being phased out and slow being replaced with the newer, more accurate SCAR series. All Rangers are to be equipped with a SCAR-H or SCAR-L by 2011.

Multiplayer
In multiplayer the M4 becomes available at Level 4, when Create-a-Class is unlocked. It is very similar to the ACR, firing 50 RPM faster but having slightly higher recoil, and lower damage dropoff and accuracy. The M4's slight recoil forces the user to burst fire at long range, which makes it more suited to medium to close than the ACR. However, the ACR is still much more accurate at long range while firing full-auto. The M4A1 is generally a 4-5 shot kill in Core game modes, and about 2 in Hardcore game modes. With low recoil and a high rate of fire, the M4A1 is often found with new players or for players who have recently Prestiged. Players often fit a Red Dot, Holographic Sight, or silencer onto this gun. The Iron Sights on this gun are regarded as some of the easiest sights to use in the game, as they are quite open, meaning a player can see more of what is going on around them.

Weapon Attachments

 * Grenade Launcher
 * Shotgun
 * Red Dot Sight
 * Holographic Sight
 * Silencer
 * Heartbeat Sensor
 * ACOG Scope
 * Thermal Scope
 * FMJ
 * Extended Mags

Call of Duty: Modern Warfare: Mobilized
The M4 is featured in Call of Duty: Modern Warfare: Mobilized with two variants, the original 3-round burst M4 Carbine, and the fully automatic M4A1. The M4 Carbine and M4A1 have the same rate of fire, but the M4A1 has much more stopping power.

M4 Carbine
The M4 Carbine is almost a copy of the M16A4 found in Call of Duty 4: Modern Warfare. Notable differences are that the 3-round burst has a slower rate of fire, more compact iron sights, and a smaller delay between the bursts.

In single player, the M4 Carbine is exclusive to the level "Closing In", though it can be seen in use by allies in all the missions of the American Campaign. It produces the same sound as the M4A1, but it has a lower damage per bullet, but it will still kill in one burst. Due to its 3-round burst and only extra 120 rounds that come with it, the M4 carbine is the least ammunition efficient weapon. In multiplayer, the M4 Carbine is available by default, along with the MP5 and MP7. It is probably the least common weapon used in multiplayer, due to its lack of power - takes two bursts to kill - and ammunition efficiency. Those who do use it usually discard it when the M4A1 is unlocked, since it has much higher power and the same rate of fire as the M4 Carbine.

M4A1
The M4A1 is very similar in appearance compared to the console, and PC one in Call of Duty 4. It has the same reload animation, and it is only found with a red dot sight in single player as well, but that is where the similarities end. First of all, the weapon has a higher damage than the Call of Duty 4 version, as it can perform a one shot kill if it is aimed at the chest at any range. Second, it has a higher rate of fire, and lastly, it has almost no recoil when aiming down the sights.

In single player, the M4A1 is a starting weapon in the last few missions of the American campaign, and in the middle of the British campaign. Since it has a high rate of fire, and only 120 extra rounds to start with, it usually runs out of ammo before the end of the level. In multiplayer, it is the first weapon you unlock for the American/British faction. Due to its high rate of fire and low recoil, it is favored by most players. The lack of spare magazines usually isn't a problem, since most players die before they use up half of the magazines.

Inaccuracies

 * The SAS are not known to use the M4A1, but rather the cosmetically similar Diemaco C8SFW, which carries the Land Force designation L119A1.
 * If you attach an M203, the amount of recoil felt will be slightly increased, but not by much. This also applies with the M16A4. The effect should be opposite, however, because the M203 adds weight to the weapon, and adding weight has the effect of reducing recoil. It could be argued however, that the removal of the vertical grip on the M4A1 could be why the recoil is increased, since the amount of grip provided dampens the recoil more than the slight offset in weight with an added M203.
 * The M4A1 and the M16A4's front sights disappear when another optic is attached. In Call of Duty 4, the entire front sight and gas block is just simply removed, which would render the gun unable to fire automatically after the first shot. The shooter would then have to manually load a round into the chamber by racking the bolt. This would effectively make the gun a bolt action. In Modern Warfare 2, the front sight is instead flipped down as the featured iron sights appear to be backup iron sights (BUIS) with a flip up sight mounted directly in the gas block. However the M16A4 still retains its original front sight, meaning removal would prevent the gun from cycling automatically.
 * The M4A1 is symmetrical; though this is incorrect, because the forward assist would be on the right side, but in the in-game model there isn't any forward assist. The same applies for M16. This was possibly included because no one would go and see the right side of the weapon during the game, and so the modeling would take less time.
 * Even though the M4A1 and the M16A4 use the 5.56mm round, the M4A1 does half as much damage as the M16. Not only that, but both the M16 and the M4A1 have the same range and mobility. These inaccuracies are most likely due to the balancing of having the M4A1 being available at the start of one's ranking, as opposed to the M16A4. The M4A1, though it (like all M16 variants) uses the STANAG magazine, yet its overall ammo capacity is higher than the M16

Videos
Thumb|center|The M4A1 in action

Trivia

 * In Call of Duty 4: Modern Warfare, on the lower receiver of the M4A1, it says "BLUE4" (a reference to BluFor, the opposite of OpFor, which is applied to all NATO forces) which is the same for the M16A4. It also says, "Property of U.S. Government, Caliber 5.55mm, M4A1 Carbine" over the magazine housing. However, the M4A1 Carbine fires a 5.56mm, not a 5.55mm, and it is also used by the SAS in game. It saying "5.55" is most likely a typo.
 * In Modern Warfare 2, Roach and Ramirez seem to be the only characters to use the foregrip.
 * If the player sets the sensitivity on console versions to 10 (max) and then spins in circles clockwise (to the right), the right side of the rifle can be slightly visible, showing a much less detailed texture. This was done because that side of the rifle is not normally visible and not detailing it saves memory.
 * There is a special version of the M4A1 called the M4A1 Suppressed. NPCs use it and it can only be acquired by using cheats or picking it up in Museum.
 * In Call of Duty: Modern Warfare 2, the rifle sounds like the Call of Duty 4 M4A1 in the singleplayer campaign, but in multiplayer, the rifle sounds quite different, with a ringing in the sound.
 * In the beginning of the Modern Warfare 2 level "The Only Easy Day...Was Yesterday", the M4A1 is titled as M4A1 SOPMOD but later in the level it changes to a M4A1 Grenadier w/ Red Dot Sight and loses its Suppressor attachment after you detonate the corpses. The SCAR-H also loses its suppressor at this point. However, if you switch out the M4A1 for another rifle and switch it back after the ambush it will still have the suppressor attachment; the quirk applies for the SCAR-H.
 * When attached with the FMJ, the grip on the rifle disappears when it is dropped, reloaded or in 3rd Person but a removable olive green grip is seen when held. It is easy to see with insane look sensitivity by looking left and right and the player seems to hold the grip.
 * In Modern Warfare 2 multiplayer, the weapon's name is M4A1. However, with an ACOG scope, the name won't be "M4A1 + ACOG scope" but "M4 + ACOG scope".
 * In Call of Duty 4, the third person view of the M4A1 lacks the grip, and NPCs and players hold the weapon like there was no grip. In Call of Duty: Modern Warfare 2, the grip is visible in third person but is still not used.
 * When using the M4 with a Red Dot Sight in 3rd person, the iron sights are still present.
 * On the left of the gun the player can barely make out tally marks. The marks surpass 100.
 * The soldier on the cover of the Hardened Edition of Call of Duty: Modern Warfare 2 carries a suppressed M4A1 with a rail attached flashlight.
 * In Call of Duty: Modern Warfare 2, when the gun is picked up off the ground for the first time, the charging handle must be pulled before it is capable of firing.
 * In Call of Duty: Modern Warfare 2 the M4A1 SOPMOD can only be found in the mission The Only Easy Day... Was Yesterday.
 * Attaching the Grenade Launcher will give the M4A1 a dipping motion while aiming down the sights and panning left and right.