I'm going to log here all the small problems I have with 3D programming, hopefully so that I don't succumb to them again. Most of them are probably applicable to programming 3D in any language or platform.
Q. Why can't I see my 3D bullets, which are cylinders? They worked when they were spheres!?
A. It's because you are shooting them from the camera's location. If they are not "closed" cylinders, and you are culling the inside of the cylinder, then they are effectively invisible since the camera is not looking at the outer surface, which is the only visible part.
Q. Why can't I see anything?
A. It could be any of a million things. Is the camera at it's correct location/direction? Is the camera inside the 3D object that it is trying to look at?