The CQBs are trading off range for speed. The best CQB weapons are MP5 and shotgun. The goal of the CQB is to inflict maximum damage to an opponent, regardless of the game type. The CQB can use claymores and mines to slow down the opponents, and make them carefully cheack each corner. As they are checking a corner for mines, it's the perfect time for a CQB to outflank and open up on them. This creates a double threat. They slow down looking for mines, and have to worry about who set the mines. A personal story: In DF2, you could set an unlimited number of clays, so I did. The goal was to create a solid line of clays, in an "S" pattern. The clays would completely circle the opponents spawn, and cause them to stop and look. Every time they stopped to look, they got shot. By the time they started running to the back off the spawn to get away from the clays, there would be clays set there. After a while of setting clays, it would completely shut down whatever spawn was clayed. Extremely effective, extremely amusing too.
The MP5 is a great weapon because it is quieter, and allows for a high percentage of headshots, due to the lower recoil. The CQB can wreak havoc on an opponents plans, as they slow them down, and never allow them to gain a foothold, or throw your team into a defensive stand.