Step 1: Materials
-Tin foil & Rubber bands (you can replace this with just duct tape, although the former lasts longer)
-Lubricant (I use hair cement but I believe you can also use olive oil or Vaseline)
-Candle wax (from any generic candle)
-Candle wicks (or something similar to use as a heat source)
-Pipe that's diameter is the same size as the one desired and whose length is slightly longer (PVC works well)
Tools that are useful:
-A hot plate
-Another, shorter, section of the same pipe
-A metal bowl of some sort (I used a cut in half soda can)
Step 2: Getting Started
To prepare the mold you have to lubricate the walls of the mold with plenty of what ever you're using. After that seal one end with the tin foil and tightly wrapped rubber band. (You may also want to lubricate the foil so it doesn't stick to the wax)
You'll want to put your heat supply (if you have something solid like candle wicks) in the metal bowl along with your wax. Being sure you're in a safe place, light the heat supply and get the wax nice and hot.
When I experimented with wax I found out that if you melted it at low temperature (like with a hot plate) then it will solidify to be soft, and if you melt it at higher temperatures (to the point the wax starts boiling) then the bullets will be rock hard.
After you've melted your wax go ahead and pour it into the pipe so that it pretty much fills it up (or fills to a little over where you want the height to be, it's better to overdo since you can cut and shave later whereas wax doesn't like to be added to wax). After all of that you can put the mold in the freezer to solidify more quickly.
If you want to just make a bunch of little cylinders (not at accurate flying unless you modify them more) then get a long piece of pipe (instead of your shorter one) and follow the same procedure as you would. After you're done you may want to get a red hot knife to slice it up
Step 3: Shaping
If you want to take your bullet's aerodynamics up a notch then you can use the knife to roughly cut the shape of the tip, then use your hot plate to smooth it out.
You also want to be sure that the bullet doesn't start to tumble in flight, to do this you need to make sure that the center of gravity is closer to the tip than the geometrical center of the bullet (length wise). If it is not then cut more wax out of the cavity in the back.
Step 4: Extra Ideas
There are a variety of things you can do/add to your bullets with similar procedures such as marbles, ball bearings, nails (although it is somewhat difficult to center it and not ruin the strength of the bullet), or any other thing you can think of.