Lastly, aim at the guys feet. Youll probably miss their head if you aim there because it will fly right over them. Also remember this can shoot around corners. Pipe Bomb Launcher. Lay down a bunch of these puppies at commomly traveled points, or by your flag.
Someone crosses over, press special, they all go boom, so does the person.
A note on MIRVs. These suckers pack a wallop. But people, don't spam unless you have a reason. Most people will just run away, you'll lag the server, and you wont have any more MIRVs. Now, if there are like four Heavys at the bottom of a long vertical shaft or something, by all means, chuck all your grenades down there, and get many kills.