Double Tap

Double Tap is a second tier perk in Call of Duty 4: Modern Warfare and Call of Duty: World at War that decreases the delay between bullets by one third of the original delay. It has no practical effect on most semi-automatic weapons to players who do not have an incredibly fast trigger finger (such as the SVT-40, G3, or M14). Some slower firing weapons such as the M1 Garand and the M1014 may benefit noticeably from this perk.

Multiplayer Tactics
This perk does not double the rate of fire as the name implies. It increases it only by a third of it. This perk is most effective on weapons that rely more on ROF than individual bullet damage, as well as close quarters weapons, but it has the disadvantage of emptying a weapon's magazine quickly and increasing recoil. It cannot be reasonably used to increase the rate of fire of semi-automatic weapons as the possible rate of fire without Double Tap is already faster than almost all players are physically capable of firing. However if the player is physically capable of doing so it may be beneficial. Some players "cheat" by using modified controllers with Turbo Fire capability, which in effect converts a Semi-Automatic weapon into a fully Automatic. Double Tap with Semi-Automatic weapons can be very beneficial when used with such controllers. It makes the W1200 much more effective, increasing the pumping speed, and a hip-fired submachine gun a serious close-range threat. Double Tap is tied perfectly with Stopping Power in terms of how fast an automatic weapon kills for guns that do 30 damage. Stopping Power wins out by hundredths of a second for automatic weapons that do more, and Double Tap wins by hundredths of a second for automatic weapons that do less. This perk does have significant drawbacks, however, as it makes inaccurate and high rate of fire weapons hard to use at medium to long ranges. Effective hip-firing may require the Steady Aim perk. It also increases ammunition consumption, which generally necessitates the use of the Bandolier Perk.

Contrary to popular belief, Double Tap does have an effect on the M16A4, as it increases the rate of fire of each individual burst, but it does not decrease the 0.2 second delay between bursts.

Also contrary to popular belief, Double Tap has an effect on Bolt-Action Rifles (Springfield, Kar98K, etc.) as it increases the speed by which a player cycles the bolt. However, Stopping Power usually makes Bolt-action Rifles a one-shot kill (unless the target is hit in the limbs, has Juggernaut, etc.), so Stopping Power is generally a preferred choice for the Perk 2 slot. But if a player is an excellent Marksman who has no problem consistently getting headshots, Double-Tap will allow them to take out multiple targets more rapidly than would be possible otherwise, because with Headshots there is no need for Stopping Power to make a Bolt-Action a one-shot kill.

It has been tested and confirmed that Double Tap increases the RoF of the M2 Flamethrower (of course with the predictable increase in the rate of overheat as well).

Double Tap also affects the M1014. While it is indeed a Semi-Automatic weapon, there is a noticeable delay in how quickly each shot can be fired since it has a capped Rate of Fire of 300RPM. Double Tap shortens this delay, allowing the M1014 to be fired considerably faster. However, the M1014 only has a capacity of four shells, and the magazine will be exhausted in less than half a second if fired as quickly as other semi-automatics. It also effects the W1200 as it will lessen the time to pump the gun. This is true for the M1897 Trenchgun as well.

Due to the 1.4 Patch for consoles, all semi-automatic weapons (Except the M1014) in Call of Duty 4 had their fire rate ceiling capped at 444 RPM. Double Tap gives leniency to the fire rate cap and allows firing at a rate somewhere between 600 and 800 RPM.

Double Tap also increases the speed in which you can plant Claymores and throw C4 very slightly as well.

Trivia

 * Double tapping is a shooting technique in real life of squeezing the trigger of a weapon twice in quick succession to deliver two shots to the same target zone, though it is used only with semi-automatic fire, as fully automatic fire on most weapons already fires faster than any human can squeeze.
 * Double Tap is featured in the three zombie maps Verrückt, Shi No Numa, and Der Riese as Double Tap Root Beer.
 * Double Tap returns in Call of Duty: Modern Warfare 2, but as an attachment called Rapid Fire (which can only be equipped on SMGs) rather than a perk.
 * Double Tap has no effect on the turrets of Tanks in Call of Duty: World at War.
 * Like the Deep Impact perk in Call of Duty: World at War, the icon shows the complete cartridge being fired, instead of just the bullet.