Glue one ball to the bottom of the cut-off portion of the bottle neck. Hot glue three ping pong balls around the sides of the bottle top. Once dry, spin the toy using the bottle top as the handle.

As you would expect, the gun is powered by compressed air housed in a length of 3 inch schedule 80 PVC pipe ... propelling the muzzle-loaded ping pong ball at supersonic speeds.

An curved arrow pointing right. The ITTF (International Table Tennis Federation) has released a video showing the manufacturing of ping pong balls and it's incredibly satisfying to watch.