Call of Duty 4: Attachments

These items can be attached to the specified weapon classes with the exceptions of the Desert Eagle and MP44. All equipment except for the grenade launcher and pistol silencer must be unlocked for each individual weapon by completing the Marksman (kill quota) challenges for that weapon. The kills needed to unlock the equipment are listed next to the equipment names.

Grenade Launcher

(assault rifles) (replaces Tier One perk): The n00b tube! Equip this attachment with 5 to bring up the grenade reticule, and fire. The impact grenade won't arm until a second or two after leaving the barrel, so aim for at least medium-distance targets. The exception is impact kills. If you can hit someone up close with an undetonated grenade, they die instantly! The kill icon is rather amusing

Damage: 155-25 / 135 Direct Impact
Range: 0-300
Fuse/Detonator: 375 Range To Activate
Other: Will not detonate under 375 range 

Silencer

(assault rifles 75, SMGs 75, pistols): A silenced weapon suffers a 2+ penalty to range and an unspecified minor penalty to damage, but when fired it won't appear on enemy radar. I believe the silencer reduces recoil somewhat as well. Use if you don't want to be detected as easily.

Damage: Minor Penalty
Range: 2+ Penalty
Other: Allows to player to go undetected, but can still be seen by UAV if not using UAV jammer 

Red Dot Sight

(assault rifles 25, SMGs 25, LMGs 25, shotguns 25): Replaces your weapon's iron sights with a battery-powered laser red dot sight. If you have trouble lining up shots easily with the iron sights, switch to the red dot. The laser dot will obscure your target at long range, but it's bright and easy to aim quickly. I always use this if I don't need any other attachment for my primary weapon.

Type: Precision Reflex Sight
Other: Great attachment for any weapon that can use it. Allows the use of perk 1, unlike some other attachments. 

Grip

(LMGs 75, shotguns 75) (replaces Tier One perk): Increases weapon accuracy by 3 and therefore decreases recoil. A considerable benefit for high-recoil weapons if you don't mind losing the Tier One perk; not really necessary for the relatively low-recoil SAW LMG.

Pro: +3 Accuracy
Con: Cannot use perk 1.
Other: This is a great attachment for the M60. The M60 has the most powerful shot out of all of the LMGs, 
but has a problem with recoil and not being so accurate. If you put grip, stopping power and deep impact, the M60 turns into a monster if played correctly.

ACOG Scope

(assault rifles 150, SMGs 150, LMGs 150, sniper rifles 100) Advanced Combat Optical Gunsight. A telescopic sight intermediate between the iron sight/red dot zoom and the sniper scope zoom, with a reticule illuminated by radioactive tritium. Decreases accuracy by 1 and increases range by 2+. Use with fairly accurate weapons that you prefer to use at long range if you can't line up or reach enemies with the iron/red dot sights.

Accuracy: -1
Range: +2