Attachments are mods for your weapons (Except melee and most specials) that change how it behaves. Only two functional attachments and two cosmetic attachments can be put on your weapon at a time, so long as they don't use up the same "spot" on your gun, e.g. you can't have two scopes at once.
- Sling: Carry your weapon from a sling for faster draw times. (Will change the model of your character to have a sling with that weapon on your shoulder when the weapon is equipped, but not being held.) Not available for sniper rifles, specials, pistols, revolvers, or machine pistols except the TEC-9.
- Holographic Sight: Picatinny rail sight that increases accuracy. Available only for SMGs, carbines, assault rifles, and machine guns.
- Extended Magazine: Larger magazine for more less reloading and more shooting. Available for everything but sniper rifles, shotguns, and specials.
- Drum Magazine: Large drum magazine for an insane amount of ammo in each mag. Also makes belt fed machine guns reload faster, but hold (Usually) less ammo. Available only for machine pistols, non-mag fed shotguns, assault rifles, machine guns, and submachine guns except:
- Henry Mare's Leg, P90, Calico M960, Vector, AR18, MP44, M1 Carbine, and Calico M100.
- Jungle Style: Tape two magazines together for faster reloading. Available only for weapons with magazines except pistols and machine pistols.
- Action Hero: Hold any combination of weapons, even those in different classes, in two hands. Available for all weapons except specials.
- Nickel Plated Bolt: Increases the rate of fire. Available for only automatic weapons.
- Optical Zoom: Change magnification on scopes when aiming using the right stick/mouse wheel. Only available for snipers.
- Suppressor: Reduces noise made by weapon, but also reduces range. Available for SMGs, carbines, assault rifles, machine guns, snipers, pistols, and machine pistols.
- Foregrip: Reduces recoil. Available for assault rifles, carbines, SMGs, and machine guns.
- Slug: Replaces shotgun pellets with a solid lead projectile for higher damage with no spread. Be accurate with it, especially if you have to pump or cock your shotgun after each shot. Only available for shotguns.
- Grenade Launcher: Underbarrel M203/M320/GP25 (Depending on weapon; doesn't affect performance) that can be switched to by pressing left on the D Pad or C on the PC when on foot. Available only for assault rifles and the M4 Carbine and HK416.
- Drive By: Fire any weapon in your inventory from a car except the Flamethrower, Minigun, MGL and Gatling Gun.
- Flat Top: Removes carry handle for a clearer sight picture, but leaves only the front sight. Available only for the M16A3, M4 Carbine, and Olympic Arms K23B.
- Harper's Charm: Boosted rate of fire with no accuracy penalty. Available for everything except explosives upon completing the story.
- Kat's Charm: Boosted damage. Available for everything except explosives upon completing the story.
- Tennant's Charm: Extremely little recoil. Available for everything except explosives upon completing the story.
- Heat Shield: A heat shield mounted on the top of the barrel. Available on assault rifles, SMGs, snipers, carbines, shotguns, machine guns, and pistols with exposed barrels.
- Barrel Shroud: A barrel shroud covering all of the barrel. Available for snipers, SMGs, assault rifles, carbines, machine pistols, and machine guns.
- Folding Stock: A folding stock over the default stock. Available for assault rifles, SMGs, shotguns, carbines, machine pistols, pistols, and machine guns. (Some assault rifles and SMGs use adjustable or collapsable stocks instead.)
- Stock Delete: Removes the stock. Available for any guns that come with stocks including specials.
- Night Sights: Adds glowing dots to the sights. Available for any gun except snipers and specials.