Recoil

Recoil is the movement of a weapon caused by firing the weapon.

This movement causes the aim of subsequent shots to suffer unless the user pauses between shots to re-aim the weapon.

In Game
Call of Duty: Modern Warfare 2 represents recoil in three different ways:
 * 1) Visual recoil - While firing, the weapon moves slightly on the screen. This movement is bi-directional meaning, for example, if the gun moves to the right it will quickly move back to the left if the player keeps firing. If the player stops firing, the weapon will quickly reset back to the original aim point. The visual recoil does affect accuracy as rounds fired will always strike where the reticle or front sight post is on the screen, regardless of the angle at which the barrel is pointing and whether the sights are aligned. A good example is the Desert Eagle as the barrel points at an extreme angle during the recoil animation and the sights are clearly not aligned, but if fired during the animation the rounds will still strike where the front sight post is.
 * 2) Accuracy recoil - Subsequent shots will not hit the center of the crosshairs.
 * 3) Aim recoil - While firing, the crosshairs will actually move from the original aim point. This movement is directional meaning it will never counteract itself. That is, a weapon that aim recoils up will only ever aim recoil up, never down. This type of recoil can be countered by manually adjusting the aim through the mouse on PCs or the right stick on consoles. When available, the Grip reduces aim recoil.

Some players claim that visual recoil does not actually affect where bullets will hit and that any deviation from the original aim point is actually caused by accuracy recoil. This is very hard to confirm or deny as visual recoil happens so quickly it's impossible to correlate with shot placement.

Some weapons, particularly sniper rifles, exhibit "sway." Sway is very similar to aim recoil but since it is not caused by firing the weapon it is not technically recoil. Sway affects every shot, while recoil affects the aim of all shots after the first.

Examples
The Barrett has both accuracy and aim recoil. After firing, the crosshairs will move to a different aim point. This is aim recoil. If the user fires while the crosshairs are aim recoiling, the shots will not always hit the center of the crosshairs. This is accuracy recoil. Accuracy recoil is most noticeable when using an ACOG Scope with the Barrett as the ACOG reduces aim recoil but doesn't affect accuracy recoil. That is, the crosshairs will have stopped moving (aim recoil) but firing too quickly still results in shots missing the center of the crosshairs (accuracy recoil).

The RPD has all three types of recoil but adding the Grip removes aim recoil. With the grip and fired in automatic mode, the weapon will shake side to side as well as slightly up and down, causing a rectangular pattern. This is the result of accuracy or visual recoil.

The results of recoil from most weapons can be viewed here:. Note that it is not always possible to tell which type of recoil is causing the bullet deviation from the original aim point.

The ACR has almost no recoil. Despite a small visual bounce, the iron sights reset perfectly to their original spot after each shot. However, there is mild accuracy recoil, as not every shot will go through the same hole though the grouping is very tight.

Precision versus Accuracy
Some players make the counter-intuitive argument that accuracy recoil actually helps inaccurate players hit their targets. The simplest explanation is to think of a shotgun: the wider the spread, the more likely a poorly aimed shot will hit. More scientifically, this argument could be compared to the scientific principle of precision versus accuracy. Basically, precision refers to the closeness of grouping of shots where accuracy refers to how many shots actually hit the target. It's easy to see how a high rate of fire weapon that is completely imprecise (spraying bullets everywhere) may occasionally be accurate by pure luck. And an extremely precise weapon, such as the Intervention, could be extremely precise but wholly inaccurate (all the shots miss in the same way.) The more skilled the player, the more precision they should desire.

An interesting example of this is to compare Modern Warfare 2's M16A4 with both the Red Dot Sight and Holographic Sight. Regardless of sight, the weapon does the same base damage but the Holographic Sight is more precise. However, some players actually find the Red Dot Sight more accurate, as the precision of the Holographic Sight is actually a hindrance to accuracy for some.