An Attachment is an enhancement, modification or accessory for a weapon. The attachments available have grown since the early Call of Dutyentries, which only included accessories such as sniper scopes.
Until the release of Call of Duty: Modern Warfare 2, weapons could only have one attachment in Multiplayer. In Campaign, weapons frequently have several attachments, such as the SOPMOD for the M4A1. In Modern Warfare 2, the Blingperk allows users to use two attachments on the user's primary. Unlocking the Pro version allows the user to put a second attachment on their secondary weapon as well.
In Call of Duty: Modern Warfare (2019), all weapons, barring launchers and specials, can have up to five attachments via the Gunsmith system. There is no way to equip more than five attachments on a single weapon. In Modern Warfare (2019), almost every attachment has at least one negative effect, whereas in older games, few attachments had any downside.
Optical Attachments replace the standard Iron Sights that most guns possess. Optics aim to improve the view of the player while aiming, either by enhancing the zoom-in effect or allowing for greater visibility of the battlefield. Attaching an Optic can be especially helpful if a weapon obscures the Player's view while aimed down the sights.
Some scopes, however, can cause certain detriments to balance their benefits: they can lengthen the time it takes in the transition from hip-firing to ADS, and some block out all peripheral vision, allowing the player to see only through the comparatively small gun-sight window while aiming.
Fire Rate
The fire rate and firing mechanisms of a weapon can be customized in many ways. Rapid Fire first appeared in Call of Duty: Modern Warfare 2 and acts as a replacement for the Double Tap perk from previous titles.
Other Attachents within this category include Select Fire, allowing a weapon to switch fire mode between semi-automatic and full-automatic, and converting weapons to alternative fire rates. In Call of Duty: Ghosts, the attachments Semi-automatic, Burst Fire and Automatic Fire were added. Later games with the Gunsmith system mostly did away with this, as most weapons such as assault rifles, light machine guns, and submachine guns tend to have a built-in fire selector. However, some magazine attachments do alter the weapon's fire mode or rate.
Barrels
Barrel-focused attachments include Suppressors, which hides gunfire from the mini-map, and others such as the Long Barrel and Muzzle Brake. Later games in the series with the Gunsmith system now have entire handguard and barrel replacements, doing away with generic long barrels, and now feature a large variety of muzzle devices that are seperately equipped barrels.
Grips
Grips have been Included in all main games since Call of Duty 4: Modern Warfare, and are sometimes known as Foregrips. The Grip reduces a weapon's recoil while firing, allowing for better accuracy during gunfights. Gunsmith-era games have multiple or even dozens of different types of grips, all having minor or major differences between them.
Under Barrel
The view when using the M203 variant.
The Grenade Launcher first appeared in Call of Duty 4: Modern Warfare and can be mounted on some Assault Rifles. They are under-slung, meaning that they attach to the rifle along the bottom of its barrel over the handguard, and are designed for the shooter to pull their trigger while holding the weapon's magazine as if it were a pistol grip.
Other under barrel attachments include the Shotgun, sometimes called the Masterkey, the Flamethrower and the Bipod.
Magazines
Includes any modification to a weapon's magazine, such as Extended Mags, Fast Mags and Hybrid Mags. In later Gunsmith-era games, magazine attachments can include a large variety of drums, flip/"jungle-style" magazines, and even smaller magazines than default, often with unique effects.
Ammo
FMJ, abbreviation for Full Metal Jacket, first appears in Call of Duty: Modern Warfare 2 and reduces the amount of damage lost while shooting through cover. FMJ also has the adds the effect of increasing damage towards equipment and vehicles. Other types of ammo such as Armor-Piercing appears in Call of Duty: Ghosts. In Gunsmith-era games, ammo types are wildly variated, having multiple different ammo types for nearly all weapon classes.
Stocks
Includes optional Adjustable Stocks that increase movement speed while aiming down sights, or stocks that reduce recoil.
Akimbo
Two B23Rs being used with Dual Wield
Dual Wield appears in Call of Duty: Black Ops and several games after. It allows the Player to wield one of the equipped weapon in each hand, replacing the ADS button as the trigger for the left-hand gun. In addition, the hipfire accuracy of the weapons is also significantly reduced. SMGs, Handguns, Machine Pistols and the Ballistic Knife can be dual-wielded in select games.
Accessories
Some attachments do not actually alter the weapon they are attached to in any way, but rather alter another capability of the player or add a new capability entirely. They include attachments such as the Heartbeat Sensor, which displays as a small screen at the bottom left of the HUD that pulses periodically to reveal nearby enemies. Other accessories include the Tactical Knife, Bayonet, Flashlight, Laser Sight and the Ballistics CPU.
Detachments
Although classed as an attachment, part of the gun has been removed, so it can be considered a Detachment. They include the Sawed-Off, which removes the end of the barrel. This increases the damage of the gun, but at the expense of both accuracy and range.
There's also the Snub Nose, the revolver equivalent where the barrel is shortened. This decreases the recoil of the gun, but at the expense of short range damage. Another example is the Iron Sight, which replaces the scope of a weapon and No Stock, which removes a weapon's Stock entirely.
