Stopping Power

Stopping Power is a Tier Two perk in Call of Duty 4: Modern Warfare, Call of Duty: World at War, and Call of Duty: Modern Warfare 2 that increases the amount of damage of a user's primary and secondary weapons by 40%.

The effects of this perk are canceled out by the Juggernaut perk in Call of Duty 4 and Call of Duty: World at War. Stopping Power will not increase the damage of explosives, such as C4, Satchel Charges, Bouncing Betties or Claymore Mines; this is accomplished with the Sonic Boom, Fireworks, or Danger Close perk. It also has almost no effect in Hardcore mode, with the exception of a few weapons, most of which are in Call of Duty: World at War.

Call of Duty 4: Modern Warfare
In Call of Duty 4: Modern Warfare, Stopping Power is very popular with the M16 and most sniper rifles. It is also the most commonly used perk in the game because of its extremely direct effect on combat. However, it is not advisable for use with shotguns, as they are already very powerful without it. Stopping Power is also more ammunition efficient, as it decreases the number of shots required to kill a target.

Call of Duty: World at War
Stopping Power is completely unchanged from Call of Duty 4. It is very effective when combined with rifles (excluding the unscoped M1 Garand, where it has little effect) and bolt action rifles. When used on any bolt action rifle, one shot can kill an enemy if it hits them in the stomach or above, excluding arms, with or without a Sniper Scope.

Call of Duty: World at War is the only Call of Duty game in which Stopping Power is useful in Hardcore game modes. The MP40, which is one of the worst weapons in the game for Hardcore because it has high recoil, a fairly low rate of fire, and is likely a two shot kill, becomes very effective when used with Stopping Power because it becomes a one shot kill at any range. The PPSh-41, which is somewhat underpowered in Hardcore because it kills in two to three shots depending on range instead of one or two like other guns, becomes extremely potent with Stopping Power, which makes it a one to two shot kill with a very high rate of fire and low recoil. The FG42, which is already very effective in Hardcore due to its mobility, low recoil, high rate of fire, and fairly long one shot kill range, becomes a one shot kill at any range with Stopping Power. These are the only three weapons in the game that ostensibly benefit from Stopping Power in Hardcore.

Call of Duty: Modern Warfare 2
Stopping Power made its return again in Call of Duty: Modern Warfare 2. It again is found in the second tier and is unlocked from Level 4 online. It has an almost identical picture to that of the Call of Duty 4 Stopping Power picture.

The Pro version is unlocked after achieving 250 kills with a class using Stopping Power. It gives the user increased bullet damage against enemy vehicles such as Harriers and Pave Lows - however this is not useful as bullet damage is heavily decreased against such heavily armored vehicles, and the vehicles will still attack a player using any Tier 2 perk apart from Cold Blooded. However, the damage increase from Stopping Power Pro can help in taking out UAVs and Counter UAVs.

Using Stopping Power in conjunction with a silencer attachment on sniper rifles or LMGs will, for all intents and purposes, negate the other's effect on the weapon's damage. The silencer attachment on the aforementioned weapons will reduce their damage while Stopping Power will essentially bring it back up to normal levels.

On Hardcore, using Stopping Power will make the Vector a one hit kill at close range, and make the USP .45 and M9 a one hit kill at all ranges.

Trivia

 * The name of this perk comes from the real-life colloquial term "stopping power", used to describe the ability of ammunition to sufficiently incapacitate its target (or, more simply, to stop from moving). In general, caliber correlates directly with stopping power, though a round's design is also a factor (as is the case with hollow point or explosive-tipped ammunition).
 * Of the three games which feature perks, Stopping Power is the most commonly used. It is also one of four that has carried over to each game.