The M16 is fully automatic in the campaign. It is the starting weapon in Operation 40, where it is equipped with an ACOG scope and M203, as well as being the starting weapon in S.O.G., where it is equipped with a Masterkey. It can be found throughout S.O.G. with different attachments. An M16 can also be found in Crash Site off the bodies of dead teammates. Strangely, the M16 in this mission has no firing or reload sound (most likely a glitch). Overall, the M16 has low recoil, a high rate of fire, and medium damage.
The M16 fires in three-round-bursts in multiplayer, like the M16A4. It is part of the default "Assault" class. After having unlocked Create-A-Class, it does not need to be purchased with COD Points.
The weapon has high damage with low recoil, offset by mechanical burst-fire, meaning it is most effective at medium-long range, especially since it maintains its damage up to longer ranges than all other assault rifles. However, the forced delay between each burst makes it less effective than automatic weapons at close range. All three rounds must hit at close to medium range for a kill, while four rounds are needed for kills at long-range, meaning that usually two bursts are needed at long range. However, if all three rounds hit, and one of them is a headshot, then it is capable of a one-burst kill at long range.
The M16 is, for the most part, the same as its Modern Warfare incarnations, although its default range is longer. It is, however, slightly less effective due to the lack of Stopping Power, as more than one burst on target is needed for a long-range kill.
The Infrared Scope and ACOG Scope actually lessen recoil, which is different from the rest of the weapons when equipped with those two attachments. The M16 with any attachment besides the grenade launcher has a solid color on the heat shield.
The M16 is available in Nazi Zombies, it can be bought off the wall for 1200 points. It is found near the power in Kino Der Toten, in the tunnels in "Five", and near Speed Cola in Ascension. Similar to Multiplayer, it is a 3-round burst weapon. The M16 is useful in middle rounds. If going for headshots the M16 is useful up until round 10, where it should either be Pack-a-Punched, or replaced with a better weapon.
When upgraded in the Pack-A-Punch Machine, it becomes the "Skullcrusher," making it fully automatic, increasing damage, and adding an under-barrel M203 Grenade Launcher. The Skullcrusher is useful if going for headshots up to rounds in the early twenties. The M203 is good for taking out large groups on zombies.