Rappers aint be dumb
Ahhh... Y'all'd be suprised at how much effort goes into true freestyling... Try it sometime. Just go ahead and rap for about 5-10 minutes to some random beat, making it up as you go along.
As for 50c, who knows. Gotta have that voice first. I think he's grunting or something. Wear a hockey mouth guard too. Rap while taking a dump, but hold it for three days first. Eat lots of peanuts and popcorn. And cheese for longeivity. Get kinda buzzed on malt liquor. If you weigh 200lbs or so, 4-5 cold ones oughtta do it. Wire your studio long before this step. Helps to have hookers probably, or just Eminem on his knees sucking you off while you spit your verse. Wear a bandana over one eye, and maybe a cape too. Have a TV set on with porn or just big booty dancers on widescreen while you write. Get angry but feel satisfied with it.