FMJ

Full Metal Jacket, often shortened to FMJ, is a weapon attachment in Call of Duty: Modern Warfare 2. Its effects on penetration are completely identical to those of Deep Impact from previous Call of Duty games. It does not increase damage against exposed targets, although it does show a damage modifier when adding FMJ as an attachment. Instead, it allows the bullets to penetrate thicker surfaces and reduces the amount of damage lost when shooting through materials.

If a player fires a weapon with the FMJ attachment, the bullets will be red tracers and a small rain of sparks will shoot from the bullets' impact point. This makes them easily visible so others can tell whether or not an enemy player has the FMJ attachment, while also changing the sound of the bullet impact. For some weapons, bullet holes appear larger while using FMJ. It is also worth noting that while it does not make the bullets themselves louder, the impact of an FMJ bullet makes very audible sounds that any player within ear-shot can hear, even if that player is using FMJ in conjunction with a silencer. Because of this, if the player hits a surface when targetting an enemy, the enemy might hear the shot and escape, or turn and shoot back.

In game, the FMJ is effective on multiplayer maps with lots of cover, such as Skidrow, the offices in Highrise, and the bunkers in Afghan.

FMJ on a Sniper Rifle causes the bullet animation to appear to "spread", making it much easier to see where shots fired from a FMJ-equipped sniper rifle come from.

Getting 40 bullet penetration kills with the FMJ unlocks Extended Magazines for that primary weapon.


 * Shooting through windows is a highly effective way for a sniper to get FMJ bullet penetration kills for his sniper rifle (especially the two higher damage rifles, the Intervention and Barrett .50cal). If a sniper can get a one-shot kill (Stopping Power makes this easier) with their first shot through the window, it will only crack. The sniper can then take a second shot through the window (it may help to find a decent-size, uncracked piece of the window through which to view a high-traffic area) and, hopefully, get a second one-shot kill, making each window potentially worth two FMJ bullet penetration kills.

Trivia

 * FMJ is one of three attachments that do not appear in campaign, the others being Rapid Fire and Extended Mags (although some weapons have larger mags without the attachment being named)
 * The MG4 and M240 have an incorrect pickup name and inventory name; they appear as "Explosive Rounds." The aesthetic properties of this attachment are more in line with this name.
 * For any weapon, firing through a window, grated floor, and even other players with FMJ counts as a penetration kill.
 * In-game, FMJ bullet holes are round. Non-FMJ rounds make elliptical holes.
 * FMJ is one of the few attachments that are available for every type of weapon except Launchers, Grenades and Knifes.
 * This attachment is unneccessarily used by many players; the stat bars show an increase in damage with the attachment which is false, and only decreases the lost damage while shooting through cover.