It is an M16A4 rifle, with the upper receiver of an A4 and lower receiver of an M4A1 Carbine. It is capable of fully-automatic fire, but semi-automatic fire allows for more accuracy and conserves ammunition, a very scarce commodity. It has a collapsible foregrip under the barrel.
The assault rifle is seen throughout the game in the hands of the military and the Salt Lake City Fireflies. The Fireflies and the Military always fire either in bursts or on full auto, making them very dangerous foes.
Joel is unable to obtain one when facing the military when escaping Boston but can pick one up at the end of the game (during The Firefly Lab) when storming the Firefly compound to rescue Ellie. Most Fireflies drop it. It is the only fully automatic gun obtained in single player.
It can hold 30 rounds and you can carry up to 120 bullets, 30 loaded and 90 in reserve. If playing on a difficulty above hard, ammo is more scarce; you only obtain 9-15 rounds per pickup compared to 30 on lower difficulties.
The assault rifle is available for purchase in Factions. To unlock, the player needs to collect 900 supplies. It costs three loadout points and requires 350 parts to purchase, or 270 parts with the cheaper purchased weapons booster. It has a 20 round magazine rather than a 30 round magazine, and ammunition must be purchased in sets of ten. Only fifty rounds may be carried by the player at any time. The ammo costs 420 Parts for every ten rounds and increases by 70 Parts for every purchase.
The assault rifle does the same damage per shot as the 9mm Pistol, taking five body shots, two headshots, or one headshot and two body shots to kill, but with a very high rate of fire. Because of this, it's very easy and to use up all of the ammunition quickly, so it is recommended to fire in bursts unless in close proximity. It does fire slower than the Specter but it isn't silenced, so one has to choose what they want; accuracy or stealth. Despite its high rate of fire and expensive ammunition, recoil is very low, and it can reliably hit targets at most ranges, making it well rounded in almost any scenario. This does mean it lacks a specialty, however; it doesn't really excel in any particular situation.
Like the Specter and Shotgun, ammo is both expensive and expended quickly which means using the "cheaper ammo" one-use booster is very helpful when using this weapon. Alternatively, one could equip the Full-Auto Rifle instead, as this does essentially the same thing as the Assault Rifle but is much cheaper and is specialized for close-range combat.
- Joel pulls the charging handle to chamber a round when reloading a half-empty magazine; this is not necessary, as a round is already chambered.
- Joel and Tess oddly do not pick up the assault rifles from the dead soldiers early in the game, when they first found out that Ellie was infected. This can be justified however, due to the fact that they were forced to run when the military appeared, and the ammunition needed for it is hard to find early on.
- This and Ellie's Pistol are the only guns in the game that cannot be upgraded, as they can each only be used in one chapter.
- The Assault Rifle is based on the M16A4 rifle, which is closely related to the M9 rifle that appears in the Uncharted series, also made by Naughty Dog.