I Guess almost everyone uses this build but incase you didn't know HERE IT IS!
Lots Of Shooting, No Reload! is kinda my idea for this build, of course eventually you are going to need to reload but in Shipment i dont think you stay alive long enough to use up a whole clip of the M6OE4 . Martyrdom is basically self explanitory on why you need it in Shipment, you die you kill like 2+ people because of Martyrdom (well i usually do). RPG for Helicopters or just killing people with it, which i dont recommend for Shipment. Double Tap i think is great for shipment so you kill people faster, even though it makes it harder to aim i dont think aiming very good is such a big deal in Shipment. VARIANTS:
RPG can be switched out for Frag x3 which is very usefull in shipment.
you could also use an RPD in case you dont have the M6OE4, i dont recommend the M249 saw because it doesn't have a good amount of Damage campared to RPD and M6OE4.
Double Tap could be switched out for Juggernaut or Stopping Power.
incase you don't have Martyrdom i would suggest Last Stand.
Ok the other day me and my friend made a build on COD4 and when we tried it out it worked pretty well, I call it "The Assasin!"
my idea for this build combo was being almost invisible and never turning up on the radar, so basically killing somone with a bunch of people around and them saying "where did he/she go?" and others saying "WTF!?" and you come up behind them and knifing them in the but hole!, and i think its pretty awesome. works great practically everywhere but especially in Free-For-All during those quiet moments, also in Search and Destroy or Sabtoge when you can Disarm or Plant the bomb without the other team noticing untill its too late.
If your not a Fan of Sub guns, then i came prepared, an AK-47 with a silencer worked out pretty good.
For extra sneakiness you can switch out Martyrdom for Dead Silence.
i do recommend using Bandolier when you have a Sub Machine gun but you can switch it out for Claymore's (putting them in random doorways or other places where people usually walk by, FTW)
COD4 online has something called Prestige mode when you reach level 55. what this is, when you do go into prestige mode (from level 55) you go back to level 1, you may notice that your rank symbol changes this is because your a higher rank (duh) and from now on your rank symbol changes from now on every time you go to prestige. Also when you go into prestige mode all your challenges are reset (you have to do them all over again) and so are you weapons (so basically you are starting all over again). here are all the rank symbols depending on what prestige level you are in.