M16A4

The M16A4 is a gas-operated, air-cooled, magazine-fed assault rifle chambered for the 5.56x45mm NATO cartridge, and is the current standard issue rifle of the United States Marine Corps and some United States Army units. It is the current iteration Eugene Stoner's original design, preceded by the -A3, A-2, and -A1 variations. The M16A4 rifle differs from the M16A2 in that it has a MIL-STD-1913 Picatinny rail under the removable carrying handle which allows different types of optics to be mounted on the top of the receiver, as well as a thicker barrel. There are also Picatinny rails mounted on the handguard to allow lasers, flashlights, foregrips, and grenade launchers. The M16A4 is capable of semi-automatic and three-round burst fire. The US military purchases M16A4s from Colt and FN Manufacturing with most M16s in recent orders being made by FN. In addition, M16 receivers for sniper variants and special purpose weapons have been procured from ArmaLite and Knight's Armament Company. The M16A4 is light and accurate, but requires frequent cleaning, partially because it is susceptible to dirt, but also because its internal mechanism lacks a piston; the gases strike the bolt of the rifle directly. This method of operation results in a lighter, simpler rifle, but causes fouling issues as carbon is blown into the chamber of the weapon.

History
The M16 was originally designed in 1957 by Eugene Stoner as the AR-15, a 5.56x45mm variant of his earlier, and unpopular, AR-10 in 7.62x51mm. It was accepted by the U.S. Army in 1961 and saw use in Vietnam, where it was generally unpopular due to fouling problems caused by the weapon's direct gas impingement system and the Army using a new type of propellant the weapon wasn't originally designed to use. This led to the design and adoption of the M16A1, which featured a forward assist. This feature, combined with regular maintenance of the weapon, helped alleviate jams and other problems caused by fouling.

The M16A2 rifle was adopted in the 1980s. The M16A2 was followed by the M16A3, which reverted to the full-automatic option. The M16A3 saw little use in infantry, but was used in some special purposes by the Navy (mostly by the SEALs and Seabees).

The M16A4 and the M16A2's carbine variant, the M4, are in wide use by United States military forces, particularly Marine Corps. The Army now primarily issues the M4, which has not seen widespread use in the Marines.

Due to the highly modular nature of AR-15 and M16, numerous derivative rifles exist, some of which even convert it to a different weapon, such as the SR-25 sniper rifle, the Colt SMG, The M6A4 SAW, and so on. Currently many of the rifles that are being considered for replacing the M16 and M4, are themselves M16 derivatives (The HK416, the ACR, the Colt ACCM, the M6A2, and the REC7).

Call of Duty 4: Modern Warfare
In singleplayer, the M16A4 can only be picked up during War Pig. It is dropped occasionally (sometimes with the M203) by dead Marines, and always uses iron sights. The M16A4 in singleplayer has a fully automatic firing mode though in reality the A4 variant features only three-round burst fire. It also used by Lt. Vasquez.

In multiplayer, the M16A4 is available at level 1 and fires in three-round bursts. It can be fitted with a silencer, Red Dot Sight, ACOG Scope, and M203. It is also fairly similar to the M4 Carbine, as it has the same appearance, the same iron sights, and they also share ammo with each other, as well as with the G36C, however, the M16 has noticably higher damage than the M4.

Using
It is often recommended to use this weapon from a distance as it is not considered effective in close quarters combat. When fired from the hip while moving the M16A4 is wildly inaccurate. And unlike most other semi-automatics like the G3 or pistols, which can be fired as quickly as the user can pull the trigger, the M16A4 has a forced delay between bursts. This delay effectively lowers the rate of fire in terms of adjusting aim meaning that at close range if the first burst misses the user will be dead before getting off a second burst. However, Steady Aim shrinks the hip fire reticle to sizes comparable to SMGs making the weapon fairly accurate from the hip even while moving. Thus, even at close range a Steady Aimed, Stopping Powered M16A4 user can be very effective if they can land the first, often deadly, burst.

The M16A4 is exceptionally powerful because all the bullets in the three rounds have a damage of 30-40 each meaning most of the kills will be one hit or two hit kills. When used with Stopping Power, the M16 is able to kill in one burst at any range provided that all three shots hit the target (only two are needed at medium and close range) and the target is not behind a wall or using Juggernaut.

Double Tap decreases the delay between the firing of each of the three bullets in a single burst and decreases the amount of time between bursts. With Double Tap, all of the bullets fired in a single burst are now fired at almost the exact same time. This can be somewhat useful in many situations, as there is a higher chance of all three bullets hitting the target and the shorter time between bursts makes the weapon more effective in CQB. However, Stopping Power is still considerably better, except in Hardcore modes.

The M16A4 is widely considered to be one of the best guns in the game due to its power, accuracy (due to tiny recoil and no red dot sway), quick reload, relatively quiet report and mobility. This makes it popular to use, but is also frowned upon by some players.

Call of Duty 4: Modern Warfare (Nintendo DS)
The DS variant of the M16A4 is quite different compared to the one in the console games. It fires in automatic mode (possibly similar to the M4A1), but it has a slow rate of fire. However, it does more damage per shot to compensate for this. Also, it is only available with an EOTech sight in single player.

Call of Duty: Modern Warfare 2
The weapon has returned in Call of Duty: Modern Warfare 2. It behaves almost identically to Call of Duty: Modern Warfare with some small differences. It is now unlocked at level 40 in multiplayer. Its reload animation is now identical to that of the M4A1 Carbine. To make it look more modernized, a Picatinny Rail has been placed on the carrying handle, and has a synthetic handguard with RIS Rails at the end. The back portion of the iron sights has been made thinner than the Call of Duty 4: Modern Warfare version, making using the iron sights much easier.

The M16A4 has barely been changed from Call of Duty 4. The only known difference is that the time between bursts has been increased from 0.2 seconds to 0.28 seconds, and the only other possible differences would be in recoil and rate of fire per burst. The FAMAS is essentially identical to the M16A4 except that it fires faster per burst but has an increased delay of 0.32 seconds between bursts.

In single player, the M16A4 is seen in both American and Task Force 141 missions. It fires in bursts in both singleplayer and multiplayer, unlike its Call of Duty 4 counterpart.

Weapon Attachments

 * Grenade Launcher (Marksman I)
 * Shotgun (20 kills with the Grenade Launcher)
 * Red Dot Sight (Marksman II)
 * EOTech Holographic Weapon Sight(60 kills while aiming down the Red Dot Sight)
 * Silencer (Marksman III)
 * Heartbeat Sensor (15 kills with the silencer attached)
 * ACOG Scope (Marksman IV)
 * Thermal Scope (20 kills while aiming down ACOG)
 * FMJ (Full Metal Jacket) (Marksman V)
 * Extended Mags (40 kills with Bullet Penetration while using FMJ)

Call of Duty: Modern Warfare: Mobilized
The weapon will return in Call of Duty: Modern Warfare: Mobilized.

Unlike the first Modern Warfare for DS, it can have an attachment, as it is seen with a Red Dot Sight.

Trivia

 * The words "BLUE4" and "Property of U.S. Government, Caliber 5.55x45mm NATO, M4A1 Carbine" in bold blue letters is visible on the side of the M16A4. The M16 fires 5.56x45mm NATO cartridges (5.55 is likely a typo) and the M4 Carbine was derived from the M16 series.
 * Individual bursts fire as fast as the P90 and M249 SAW, making it an unusually fast-firing Assault Rifle.
 * In multiplayer, if you attach the grenade launcher to the M16A4, the heat shield turns into the one that was used for mounting the M203 onto M16A2s. This is unnecessary, as the M5 RAS used on the M16A4 is just as capable of mounting the M203. This does not necessarily indicate that it turns into an M16A2, since it is one part that is very easy to swap out, and it still has the A4's removable carrying handle. In Modern Warfare 2, this feature is removed.
 * In single player, if you enable the "Infinite Ammo" cheat and pick up a M16A4 with the M203, the full-automatic rate of fire of the grenade launcher is very, very fast and greatly surpasses that of the M4A1. Curiously, the M203 on the M4 Carbine and the GP-25 on the AK-47 have much slower full-automatic rates of fire, about the same as the W1200.
 * The M16A4, FAMAS, and the M93 Raffica are the only guns in the Call of Duty series that are capable of firing in bursts.
 * The in-game model depicted the M16A4 having A4 upper receiver, but has an A1 lower receiver, which explains why the weapon can go full-auto in single player.
 * In Call of Duty 4: Modern Warfare (DS), the M16 has an EOTech sight in single player, instead of an iron sight in multi-player.
 * When an M203 is attached the forward iron sight changes size.
 * It usually takes two or more bursts to kill an enemy, depending on the perks the player and the target has.
 * In Call of Duty 4 DS, even though the M16 fires fully automatic for the player, allies fire it in a three-round burst. This is the same with most weapons, even those used by enemies.
 * In Modern Warfare:Mobilized, the M16 is labeled as the "M4 Carbine", even though it fires a three round burst like the M16, not M4.