M16 Assault Rifle

The M16A3 assault rifle is a Tier 2 replacement for the submachine gun with higher damage and better accuracy. It holds 50 rounds with a 360 round reserve, having less total ammo then the Uzi, but being a better overall weapon. The M16 is the best choice as a general use firearm, as it is adaptable to most situations.

Tactics
The assault rifle is a weapon that is mostly effective in medium-range combat, as opposed to the short-range auto shotgun and the long-range hunting rifle. It is a very flexible weapon, however, adept at picking off Special Infected from a distance and piercing multiple Common Infected. Because it has a high piercing power (though not quite as high as the hunting rifle), it is a useful weapon for clearing rooms full of Infected or destroying oncoming hordes.

With Valve's recent update reducing auto shotgun damage against a Tank on the PC version (the update will be released on the Xbox 360 eventually) and the assault rifle's high medium-range accuracy, the assault rifle has overtaken the auto shotgun as a weapon of choice for killing a Tank. The auto shotgun is still just as useful against nearby Infected, and in close quarters weapon choice lies to player preference.

Assault rifle ammo is easy to waste. The weapon trades ammo capacity for accuracy and damage, and this must be used to full advantage to be effective. The assault rifle generally needs only two or three shots to do its job, and any more hampers its accuracy at mid to long range. Thus, burst firing or headhunting is highly recommended at medium to long ranges as this not only helps to improve accuracy, but this also has the benefit of conserving precious ammo.

While this weapon may be useful on higher difficulties because of its tighter cone of fire being safer when firing near other survivors, this weapon struggles to keep up with the increased health of the Common Infected, requiring 4 bullets to kill one on expert, whereas a single shot from the other two weapons is still a kill. Additionally, the mid-range effectiveness of the assault rifle is shared with the pistols, meaning that taking the assault rifle sacrifices some flexibility.

In a group of four on finales, it's a good idea to have two people with Auto Shotguns and two people with Assault Rifles, get in a closet or similar point which causes the Infected to file in slowly, the two people with the shotguns crouch and shoot or melee, while the two people with the assault rifles stand behind them and fire rounds into the Infected as they approach. Be careful to note when the Tank comes, however—a Tank can easily destroy a group of four Survivors hiding in the same closet. It's best to run out and kill it in open ground, and return to the former spot when the Horde has come back.

Trivia
It is based off of the M16A3. The M16A3 rifle is an M16A2 rifle with an M16A1's fire-mode control (semi-automatic fire, automatic fire) used only by the U.S. Navy.
 * The in-game texture states that this rifle is produced by the fictional company American Armory as the M16A2.
 * It has 360 reserve ammo, so it probably originally had its real life capacity of 30 rounds.