small bbs or even green rods from knex.
All you will need:
Nerf tm darts.
Air blaster's tm Double Shot
Shells for the gun.
A thick straw that just fits the shell.
(Must be able to fit a Nerf dart inside.)
bbs or small knex rods
Step 1: The straw
the straw where the shell ends. Cut around that line so
u have a tube about the same size as the shell.
If the straw is loose place some tape around the bottom.