This is likely one of the quickest and cheapest projects that I have ever done however it will shoot with a surprising amount of force and even break thin glass and if you don't want that kind of fire power you can simply shoot mini marshmallows. Hope you enjoy this build and remember that this is at your own risk.
Step 1: Materials
For The Gun
3 - 4ft of 1/2 inch PVC or CPVC pipe
Tape (any will work and it is only for decoration)
Reducer Fitting (this is optional for a larger mouthpiece but is not necessary)
For The Darts (this portion is not necessary if you want to shoot mini marshmallows or Nerf ® Darts)
1 Pad Of Sticky Notes (lots of colours are nice)
Clear Office Tape (not packing tape)
Small Nails (optional)
Small Screws (optional)
Oil Based Modelling Clay (or poster putty)
Party Hat (any thing that is cone shaped will work it is only to help you get the right shape for your darts)
See what I mean its super easy!
Step 2: Tools
HackSaw or Pipe Cutter (to cut the PVC) (I can't find mine so I used a Wood Saw)
Screwdriver (or anything to push the putty into the cone)
Nothing Powerful, Just Be Careful With The Saw
Step 3: Cutting the Pipe
For this step all that you have to do is chose your length, (you can measure but it is not necessary) then cut using your saw. If you are using a hand saw make sure you have adequate adult supervision and if you are using a power saw make sure this is done by someone that is experienced with power tools and they are wearing proper PPE. Remember that this is at YOUR OWN RISK.
Step 4: Assembly
For this step, start with your coloured duct tape and lay it down on a work surface then place the PVC pipe on top and rock back and forth until the tape is fully applied and all of the wrinkles are out and if there are a few remaining just work them out with your fingers.
Once the Duct Tape is applied use Electrical tape to seal off the ends and create a design (if you want)
Step 5: Darts
Roll Sticky Notes around party hat to make little cones.
Tape the cones so that they will stay closed.
Trim so that the cones will fit tightly but not too tightly into the gun.
Fill the cones half way with modelling clay and compact and push to the bottom of the cone with a screw driver.
Put a nail through the clay so that the head sitting firmly and the tip is poking out like a dart.
Repeat steps 1 - 4 but instead of putting a nail you put a screw in the opposite direction.
Step 6: Final Product
This is awesome it can easily break glass and puncture cardboard so make sure you don't point it a people or any thing of value.