Modern Warfare
CoD4 Ultimate Sniping Guide
Sniping Guide: Snipers | Sniping Guide: Attachments | Sniping Guide: Techniques
Guide by Feonian - This is my guide to sniping. Sniping is nice because you can sit back, way away from the action, and quickly take out enemies. Snipers usually do not rack up many kills with their gun only. Because they are away from the action, they tend to live longer, making them more likely than others to get helicopters and air strikes. Once you get good, you can take out running targets and then keep the scope up after you fire, which makes you nearly impossible to track, even with the killcam. Snipers usually die in two ways. They either get counter-sniped, or they attract too much attention and someone throws a grenade into their hiding spot. In this guide, I will go over setting up your class, link to my guide that shows you where to snipe, and then tell you how to snipe effectively and safely. I will tell you tricks on hitting targets, how to not be seen visually, how to not be tracked via the killcam, how to beat other snipers, and what to do in various other situations.
Before you can snipe, you have to have a class. First, you should choose a gun, then perks that are compatible with the gun, and then pick out the pistol that fills in the weak spots.
BOLT ACTION VS SEMI-AUTO: This is the first choice you have to make. They both have their share of powerful and weak weapons. One is not the more powerful group. With the bolt actions, you gain accuracy, but lose the ability to fire off a second shot as quickly. If you are generally pretty accurate and are attempting many difficult shots, you will want the accuracy of the bolt actions. If you miss occasionally and would like to have the ability to make a second shot, go with the semi-auto snipers. I prefer bolt actions for regular sniping, and semi-autos for ACOG/mobile sniping. You will need the accuracy if you are camping, but at close range, you need to be able to make a second shot.
M40: This is a great rifle for normal and hardcore. The most accurate, with acceptable power, no recoil, but a low fire rate. Pick this gun if you want to be able to quickly and accurately take out targets across the map. My preference for hardcore because of its accuracy.
Here is how it rates in each category:
Power: Below average.
NORMAL: If you have stopping power on, it will kill in a hit to the head, neck, chest, and stomach. If you do not have stopping power, or if you do and are shooting a juggernaut user, it will kill to the head and neck.
HARDCORE: It will kill in a hit no matter what. Look at other factors for determining your hardcore gun.
Accuracy: Accuracy is determined by how fast the crosshairs steady and how likely the bullet is to land where you point the crosshairs. The M40 pulls up and steadies faster than any other sniper. In addition, since its bolt action, the bullet will go where your crosshairs are pointed. It is the most accurate sniper.
Fire Rate: This is determined by how fast you can get a second accurate shot off. Recoil and whether or not it is bolt action both affect these results. You can get another good shot off about every second; more at really long distances, and less at close range. 
R700: This is another good gun. Use it if you like the M40, but feel it just is not strong enough. It fires very slowly, but if you are accurate, that is all you need. This gun really thrives on the idea of one shot, one kill and does it better than the others.
Power:
NORMAL: If you have stopping power on, it will kill in a hit to the head, neck, chest, and stomach. If you do not have stopping power, or you do and the enemy has juggernaut, it will kill in a hit to the head, neck, and chest. Tied with the Barrett .50cal for the hardest hitting sniper.
HARDCORE: Will kill in a hit no matter what. Look at other factors.
Accuracy: Since it’s bolt action, the bullet always goes where you want it to.
Fire Rate: This gun has the lowest fire rate of them all. You can get an accurate second shot off about every 1.25 seconds, which is painfully slow. 
M21: Being semi-automatic, the bullet may not always go where you tell it. It usually does, but you will occasionally miss a dead on shot because of this. The M21 really thrives in being beginner friendly, especially compared to the bolt-action rifles. It has poor power, but you can get a second shot off quickly if you miss the first. By far the most forgiving sniper. If you miss with this, you are not totally screwed. This is most people’s choice for hardcore because its major downside is the power.
Power:
NORMAL: The worst amongst the snipers. With stopping power, you will kill in a hit to the head, neck, and chest. Without stopping power, or with it against a juggernaut user, you will kill in a hit to the head, and neck.
HARDCORE: Will kill in a hit no matter what. Look at other factors.
Accuracy: It is semi-auto, so occasionally you will miss dead-on shots. It is not very often, but it does happen.
Fire Rate: This has the best fire rate. You can get a second shot off in about .375 seconds, or 3/8 of a second. 
Dragunov: This is the gun you should turn to if you would rather not use stopping power. It is not affected by stopping power, so if you would be willing to have a weaker weapon than most and have a perk such as juggernaut, UAV Jammer, or overkill instead, this is the gun you should use. This is also my choice for an ACOGed sniper for it's acceptable power, and low recoil in case a 2nd shot is needed.
Power:
NORMAL: The power is peculiar because it does not gain any ability to one-hit from stopping power. Without stopping power, its power is equal to that of the R700 and Barrett .50cal. Since the Dragunov has the least recoil and highest fire rate of the three, at the same power, it is the ideal choice for anyone wanting the utility of another perk two choice. With stopping power, you will kill in a hit to the head, neck, and chest. Without stopping power, or with it against juggernaut, you will also kill to the head, neck, and chest.
HARDCORE: Will kill in a hit no matter what. Look at other factors.
Accuracy: It is semi-auto, so occasionally you will miss dead-on shots. It is not very often, but it does happen.
Fire Rate: The second best, behind the M21. You can get an accurate second shot off roughly every .75 seconds; it’ll take less time up close, and more time at a distance. 
Barrett .50cal: This is the gun most people think is the best, but it is balanced just like the others. It hits as hard as the R700, but its semi automatic, which makes it less likely to hit those difficult, long-range targets, but you can get a second shot off faster. Use the Barrett .50cal if you like power and the ability to one-hit targets, but are not always the best shot and may need to make a second shot.
Power:
NORMAL: If you have stopping power on, it will kill in a hit to the head, neck, chest, and stomach. If you do not have stopping power, or you do and the enemy has juggernaut, it will kill in a hit to the head, neck, and chest. Tied with the R700 for the hardest hitting sniper.
HARDCORE: Will kill in a hit no matter what. Look at other factors.
Accuracy: Just like all semi-autos, the accuracy is just ok. You will usually hit, but there will be the occasional dead-on shot that will miss.
Fire Rate: Roughly equal to the M40. You can get a second, accurate shot off about every second.
Click here to view the Attachments section of the sniping guide
Sniping Guide: Snipers | Sniping Guide: Attachments | Sniping Guide: Techniques