Grip

Call of Duty 4: Modern Warfare
The foregrip is an attachment to weapons in Call of Duty 4: Modern Warfare that will reduce weapon recoil. The foregrip attachment is available for light machine guns and shotguns. It is unlocked when a player achieves 75 kills with a light machine gun, and 50 kills with a shotgun. Using the foregrip attachment will replace a player's tier one perk.

Call of Duty: World at War
The grip attachment is only available for the two shotguns, the Double-Barreled Shotgun and M1897 Trenchgun. It decreases weapon recoil just as in Call of Duty 4: Modern Warfare, and as previously, replaces the player's tier one perk. Instead of the polycarbonate synthetic pistolgrip from Modern Warfare, foregrips are basically wooden handles, finished and fashioned into sticks that simply attach to the gun's gripping area. With this attachment, the Double-Barreled Shotgun has a small wood handguard under the barrels rather than a vertical grip.

Call of Duty: Modern Warfare 2
The foregrip attachment is available for LMGs and Shotguns in Multiplayer. For LMGs, the Foregrip is the first unlocked attachment (Marksman I, 10 kills). For shotguns (except the Ranger and the Model 1887, they cannot accept a foregrip), it is unlocked at Marksman III (75 kills). When attached to a shotgun it reduces the recoil but the bullet spread remains the same. When on an LMG it greatly reduces recoil allowing for much greater accuracy. Unlike Call of Duty 4: Modern Warfare and Call of Duty: World at War, the grip does not replace the Tier 1 perk.

Trivia

 * In Call of Duty: World at War, a Sawed-Off Double-Barreled Shotgun w/Grip is located just before entering the Asylum in the mission Ring of Steel, and in the Nazi Zombies game modes from the random weapon box. The shotgun is unique in that it combines two attachments on one weapon, something generally not possible in the rest of the game.
 * In Call of Duty 4: Modern Warfare and Call of Duty: World at War, some players consider the grip a waste of a Tier One perk, however, a possible way around the problem is to use Overkill with a gun that also has an attachment replacing the Tier One perk (Grenade Launcher/Rifle Grenade, or another weapon with a grip).
 * In Call of Duty 4, the M4A1 Carbine can usually be found with a foregrip (unless the M203 is attached), but it is purely cosmetic. In Modern Warfare 2, the same goes for the MP5K, TMP and Striker.
 * The Striker's model always has a foregrip, even when there is no foregrip attached, but with a different model than the actual attachement.
 * In Modern Warfare 2, a SCAR-H with a Foregrip can be found right before The Pit in S.S.D.D. As the SCAR-H already has low recoil, it does not have any discernible effect.
 * In Modern Warfare 2 multiplayer, third person character models never actually hold foregrips.
 * The SCAR-H in multiplayer was originally coded to have a foregrip, but it was taken out. However, the pickup/kill log icon still shows it with a foregrip.
 * Many people believe that using a grip on a shotgun makes the weapon more accurate and have a tighter spread. This is untrue as all the grip does is reduce recoil which usually leads skilled players to believe it is a wasted attachment as the player can adjust for the recoil quite easily on most shotguns.
 * The attachment picture for the grip in Call of Duty 4: Modern Warfare is a pistol grip and in Modern Warfare 2 is a foregrip.
 * In Call of Duty 4: Modern Warfare attachment picture (shown in the top) says it is a vertical foregrip for reduced recoil while the picture is a pistol grip.