In the second large containment room, run ahead of your team. There are two enemies with Desert Eagles who will try to surprise you around two corners, depending on the path you take.
If a target is moving make sure to lead it. If you are not making shots try to lead your target more. Also, if you are a skilled sniper try using the M40A3 over the M21. It has a slower reload time and rate of fire, but it has enough damage to kill a target in one shot instead of two or three. It also allows you to be less noticeable with less rounds being fired; so someone else cannot follow the tracer shot back to you. A good setup for the sniper is the Claymore perk, to alert you when an enemy is trying to close in on your rear, and either the Sleight Of Hand or Stopping Power, then Iron Lungs to give you more time to line up your shots.
Once you get the Red Dot Scope addon to your weapons, use it over the ACOG scope. The red dot will not enhance or take away anything and provides a better aimpoint on most weapons. The ACOG scope will actually add more range to your weapon, but take away accuracy which accomplishes almost nothing; especially so for snipers because it takes away range and adds nothing.
To level up quicker than usual, try to use the same gun until all the marksman and elite challenges are completed. They provide huge boosts and will quickly level you up to get new guns. However, do not use those guns yet. Just keep on the challenge until it has completed. The third phase of the challenge usually ends with 1,000 experience points and that will bump you up a rank almost in itself. Also, do not forget about the strange challenges like jumping 15 feet and surviving or falling 30 feet to your death. To get that one if not previously unlocked play the "Countdown" map and jump into one of the open missile silos. You will get instant experience points for simply dying. Also, remember to go prone and crouch to get those challenges as well.
To see the message, you start with Mile High Club mission playing on Veteran difficulty, Reach the part of the mission where you will require to shoot the terrorist who is holding the captive and rather of shooting him in the head, shoot any other part of the body, Mission will stop working, however you will see a secret message!
In the level where you get Nuked by the Opfor you are on the Mark19, a grenade launcher . When you are landing(Anywhere) and you're about two metres above the ground, aim as low as you can go, then shoot the ground. There is no explosion, just a bullet hole where you shot.
This is a simple glitch that an be used to dominate your opponents quickly and easily. To perform this glitch, you must select the 'Crossfire' map and make your way down to the bottom end of the street and go left where you will find a building with some sort of kichen essential eg. dishwasher, washing machine. Climb on top of this and jump onto the next floor of the building from this position. This may take several attemps but it can be done. Then from here, make another jump to the next floor. Once this is done, make your way to your right whee there is a barbed wire fence below you. Walk directly above this to the next building. Then make your way to another jump. For this jump you will have to sprint to the far left corner, into the wall and then jump. You will now be in mid-air, being able to go prone and cover a good amount of the map.
Following the 'Mid-Air Domination' glitch you can get into a superb sniping position. Follow my previous glitch and stand at the edge of the building where you can see the whole street. Looking down from the building, you should be able to see a balcony. Move to your right and jump down to it. This is a superb sniping position and hiding spot.
Collect the Intel Pieces (enemy laptop computers) hidden throughout the game to unlock the cheat options. The number of pieces you have determines which specific cheats are available.
Unlockable:
How to Unlock:
A Bad Year
15 Intel Pieces. Enemies explode into tires when shot.
Cluster Bombs
10 Intel Pieces. When a frag grenade explodes, four more will explode in a cross-shaped pattern.
CoD Noir
2 Intel Pieces. Allows black and white graphics.
Infinite Ammo
30 Intel Pieces. Reloads are no longer necessary. This has no effect with single-shot weapons such as RPGs, C4, or Claymores.
Photo-Negative
4 Intel Pieces. Inverts the colors.
Ragtime Warfare
8 Intel Pieces. Silent movie mode.
Slow-Mo Ability
20 Intel Pieces. The game slows to half speed when you melee.
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