Carbine Rifle

The Armalite/Colt AR-15 series of weapons is a lightweight, air-cooled, magazine fed, autoloading, centerfire rifle, and is probably the most famous assault rifle family ever built by the United States, first appearing in 1958 and continuing to serve 50 years later. The AR-15 is a further development of the AR-10, a 7.62mm rifle developed by Eugene Stoner. The rifle was later adopted by Colt into various successful designs for both the military and civilian markets. The various variants have been present in every Grand Theft Auto III era game, and their usage is beneficiary in almost any situation, due to the fact that the rifles features well balanced accuracy, power and ammo capacity. Since the rifle fires the relatively powerful 5.56mm NATO round, it has a noticeable recoil force, however not nearly as much as the bigger AK-47. Throughout the games the models of these firearms differ slightly, along with zoom capability, fire-rate, and power. In Grand Theft Auto III the firearm is an exaggeration of an M16A2, as it takes its appearance, however unlike the real-life M16A2 it fires in the fully automatic mode, and at an extremely high rate of fire, boasting a 60 shot magazine. In GTA Vice City, the overall realism is much improved and the weapon now looks and functions like the real life M4 Carbine, even though the M4 didn't exist in 1986, but entered service in 1995. It is meant to resemble the Colt Model 733 Carbine, a weapon that is based off the CAR-15, a carbine version of the M16. The M4 remains the same throughout Grand Theft Auto: San Andreas, and Liberty City Stories. Once again in Grand Theft Auto: Vice City Stories the gun changed to a M-16 A1 to represent the actual time era of when the game occurred, 1984.

Variations
GTA Vice City Stories (1984): M16A1, accurate by timeline and rate of fire. The M4 is mentioned in a mission by Lance Vance which is a small dialogue error.

GTA Vice City (1986): Colt Model 733, however it's called M4 in-game but that's incorrect since the M4 was not introduced until 1995. The M4 was presumably supposed to be a Colt Model 733 Carbine, a CAR-15 derivative, but the developers did not realize this.

GTA San Andreas (1992): Colt Model 733, but called M4 in-game. Same mistake as in Vice City. This version for some reason has an unrealistic reload animation that causes CJ to charge the weapon with his left hand, while the real M733 is charged with a rear mounted handle. This rendition inaccurately holds 50 rounds per magazine which is not possible with real life M733s.

GTA Liberty City Stories (1998): Colt Model 733, but called M4 in-game. Accurate by timeline and rate of fire. This version for some reason has an unrealistic reload animation.

GTA III (2001): M16A2, this version is highly inaccurate, with a 60-round magazine and an insanely high rate of fire.

GTA IV (2008): M4A1, this version is accurate, both in timeline and overall features. It should be noted that this version features a peculiar rear sight design and lacks a carry handle, causing it to be mistaken for a Heckler and Koch HK416, a similar designed weapon.

GTA III

 * Rockford, Staunton Island - Available to buy from Phil Cassidy's Army Surplus after completion of Arms Shortage ($5,000).
 * Bedford Point, Staunton Island - In the walled off area in the southeast part of Liberty Tree Offices (use the nearby Moonbeam, park it by the lowest part of the wall, climb the Moonbeam, and jump over the wall to access).
 * Cedar Grove, Shoreside Vale - On the back porch of the pink house (fourth from the west) at The Homes.
 * Cochrane Dam, Shoreside Vale - Near the top of the stairs for the west dam platform (not the top of the Cochrane Dam power house) at the base of the Cochrane Dam.

GTA Vice City

 * Prawn Island - In Studio B (behind the moon lander) at the InterGlobal Films complex.
 * Starfish Island - In the small room at the bottom of the Mansion's stairwell east of the main entrance after the completion of Rub Out.
 * Downtown - Available to buy from Ammu-Nation after completion of Rub Out ($5,000).
 * Little Haiti - In the middle of a cluster of shacks in the center of the North Haitian Neighborhood (just south of Auntie Poulet's house).
 * Little Havana - At the west side of the red and white building directly across the street west of Cafe Robina.

GTA San Andreas

 * Los Santos International Airport, Los Santos - Next to the runway, there are three white and yellow striped "ramps". Between those which are placed at the end of the runway
 * Palisades, San Fierro - Behind a house next to the beach
 * Area 69, Bone County - Behind a staircase leading to a control tower
 * Pilgrim, Las Venturas - On the roof of the hotel
 * Four Dragons Casino, Las Venturas - In front of the casino if all 50 Horseshoes are collected

GTA Liberty City Stories

 * Newport, Staunton Island - Among the containers at the docks and east of an unique stunt jump. It's located between the containers that are placed towards the Big Shot Casino.

GTA Vice City Stories

 * Vice Point - Behind the building next to northernmost empire site.

Grand Theft Auto IV
The AR-15 in Grand Theft Auto IV is referenced in-game as the Carbine Rifle. It can be purchased from the back-alley gun shops for $5,000 and each additional magazine will cost $100. It can be purchased from Little Jacob for $3,500 and each additional magazine costs $70. The Carbine Rifle can also be acquired from NOOSE officers and certain LCPD officers.

Bohan Algonquin Alderney
 * Industrial - Can be found in one of the offices inside the abandoned warehouse where the player rescues Roman from the mission Hostile Negotiation.
 * Algonquin Bridge - Can be found atop the roof of the pedestrian walkway on the Algonquin side, from the monorail station entrance.
 * Easton - Can be found well-hidden behind some trash cans on the east side of Grand Easton Terminal. The trash cans can be reached quickly through an alley on Jade St.
 * Leftwood - Can be found underneath the pier where the strip mall is situated off Beaverhead Ave. The strip mall can be seen from the cliff where Niko executes Aiden O'Malley during the mission Tunnel of Death.
 * Tudor - Can be found in a small loading dock area on the north side of the old Sprunk factory.
 * Tudor - Can be found atop the northern superstructure of the old rail bridge that spans the river which divides Tudor and the Acter Industrial Park.