The PVC dart was not actually designed by myself. You can check you the link at the bottom of this page for more info. Though modified to suit my purposes.  I have perfected it to attain maximum height and range. Its primary use is to measure the maximum range of any cannon. I'm sure you can tell it isn't the easiest device to construct.  Especially the fins. This design fits snuggly onto a 1 1/2" barrel and has a head filled with washers to give it some weight.  This projectile can also be used as a propellant-less rocket which can attain altitudes higher than what is measurable with the naked eye.

I actually made 2 designs.  The smaller one for the rifle and the larger one for the bazooka.
 

The idea for these was taken from
http://www.valuelinx.net/~dthames/bullet_design.htm