The Game Walkthrough

The sniper rifles in Call of Duty 4 are relatively powerful. with the obvious exception of the M21.
The first sniper (The M40A43), which is unlocked after leveling to level 3, is one of the most powerful. In a normal game it will most likely kill but it is possible that your opponent may survive - They may be using the perk "Juggernaut" which means they have extra health, or they may have only been shot in the foot.
The second sniper rifle, the M21, is appalling in most if not all aspects. It often takes more than 2 bullets to kill and it's accuracy is poor.
The Dragunov is the third sniper in Call of Duty 4 and is unlocked at level 22. It has similar statistics to the first sniper except it has a much faster rate of fire.
The fourth sniper, the R700, is basically an upgrade of the first sniper. It has a higher accuracy and higher damage, making it one of the most popular snipers.
The last sniper, the Barrett, has similar statistics compared to that of the R700, except it has a lower accuracy and higher rate of fire, making it probably the most popular sniper rifle in Call of Duty 4, however probably not the most used since it is only unlocked at level 49

Sub Machine Guns

Sub Machine Guns in Call of Duty 4 are, in my opinion, the best weapon that you can choose. The major advantage to a SMG is that it is mobile, you can easily move around and make it harder for your enemy to hit you. Furthermore, the majority of SMG's have a high damage rate and a moderate accuracy, which is very beneficial in close quarters combat. However, the major disadvantage to SMG's (With the exception to the P90) is that they can not carry much ammunition; This can be disadvantageous in long range combat maps. In my opinion, the MP5 is the best SMG because it has a relatively high power, accuracy and ammunition count. I find it most effective without any attachments.

Shotguns

Shotguns are remarkably underpowered in Call of Duty 4, but what they lack in range they make up for in damage. If you know how to use it, the pump action shotgun can be very effective. A popular method can be used with the W1200, it is known as "Luring". Basically, you will jump out so a enemy a long distance away from you will see you. You then move away so they can no longer see you. You wait a short period of time, and then jump back again. You should find that your enemy has attempted to follow you. They will not have the time to stop. If you are using stopping power then you should have no problem dealing with them with one shot.

Finally. The hardest way. The most boring and time consuming way. If you have no decent items, no armor-piercing bullets and no money, then here is a way to defeat the daddies. Quite Simply, find the daddy, and hit it with your wrench. As much as you can. Until you die. Once you have died, you will be revived in a nearby Vita Chamber. Simply find the Daddy again, and carry on where you left off. This method is time consuming, as well as boring as hell, but it does get the job done. Eventually. Note, this is very ineffective on Hard difficulty.