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 (for example, the M4 in Modern Warfare 2 is more closely similar to a model manufactured by Bushmaster). 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 ACR and SCAR have been trialed for general issue, but a successor has not yet been found.

Call of Duty 4
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 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 it in all missions. Surprisingly, in the SAS missions, the M4A1 SOPMOD seems to have all attachments available, a red dot sight, silencer, grip (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, and an M203.

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 fully automatic 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 silencer or a red dot sight is a good choice.

Call of Duty: Modern Warfare 2
The M4A1 returns in Call of Duty: Modern Warfare 2, and has retained most qualities and appearances of the Call of Duty 4 version. Although it seems to have more of a tactical appearance. The M4 in this game is actually very similar to the Bushmaster Modular M4 Carbine, except that the game version has a shorter barrel, indicating that it is a version built for close combat. 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 add-on. This gun also highly relates to the 6.8mm REC-7 (or known as the M468) due to the gas break barrel style and how easy it is to take down an enemy.

The Carbine has the fourth highest damage output per second, right behind the F2000 due to its high rate of fire, but still slower than the F2000 by 100 rounds. The M4A1 trades this for much less recoil and an earlier unlock level.

In multiplayer, it is the first Assault Rifle available. It handles very similarly to the SCAR-H, with similarly tight bullet grouping to the SCAR-H when using iron sights though with tighter grouping when using either ACOG or Thermal. The M4A1's added accuracy is balanced by doing less damage per shot than the SCAR-H.

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 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 kill in one shot to the center of the chest. 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 it's high rate of fire and high damage, it is favoured 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. However, they have such a large array of weapons at their disposal that it is possible.
 * 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. However, it is still reasonable for the M4A1 to have a little less damage than the M16A4 since the shorter barrel length allows for less muzzle energy.

Trivia

 * 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 person to use the grip.
 * If you set the sensitivity on console versions to 10 (max) then spin 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. (It's also in the Museum level.)
 * 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 lot more punch 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 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 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 not a grip. In Call of Duty: Modern Warfare 2, the grip is visible in third person but is still not used.
 * In Call of Duty: Modern Warfare 2 the grip disappears when a Thermal Scope is attached,but the character model still holds the gun as if there is a grip.
 * In the campaign in Call of Duty: Modern Warfare 2, when using the M4A1 Grenadier w/ Red Dot Sight variant, aiming down the sights provides further zoom than a normal red dot sight.
 * In Single Player, the M4A1 has two variants: regular with no sights attached, or a grenade launcher attached with a scope. The rifle+scope without M203 attachment is never seen in the campaign.
 * In Modern Warfare 2, the M4A1 uses the same pickup icon as in Call of Duty 4. Even though the carrying handel is missing in MW2.
 * 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.
 * In Modern Warfare 2, the M4A1 is the S-System variant, which has flip-up BUIS sights and a handguard that fills the gap in the top rail, allowing the user to place optics to their preferred eye-relief distance.