This is my first instructable so feel free to leave comments and tips.
Step 1: Materials
4 1/2" PVC 90 degree joints
1 1/2" PVC coupling
1 1/2" PVC ball valve
(I think you have discovered by now that all the PVC components are 1/2".)
1 PVC tee
1 PVC one-way valve (Look for it under the name "check valve")
1 PVC end cap
Assorted lengths of PVC pipe (1/2", of course)
Dowel that will fit into the pipe
Step 2: Assemble the Stock
(The stock also doubles as an air tank.)
Step 3: Assemble the Barrel
Again, don't cement the pieces together! (I made that mistake.)
Note: I attached a short bit of wood to my ball valve to make it easier to turn. That is what the long wood thing is in the picture.
Step 4: Assemble the Pump and Plunger
Now for the plunger: Take a dowel that is about three inches longer than your pump tube. Get your rubber stopper and make a hole in it. Put a screw through the hole and screw the stopper to the end of the dowel. The stopper should be able to fit loosely in the pump tube. Now tighten the screw and the stopper gets wider. Tighten it until it is just able to slide with effort along the pump tube. You could probably use petroleum jelly or Vaseline to lubricate the plunger and increase the seal but I had none of this so I had to do without it. Another good idea is to put a screw or nail in the top of the dowel to stop it from sliding all the way down the pump tube and getting stuck in the one-way valve. It is a pain to get it out when it gets stuck there.
Important note: DO NOT put WD-40 on the plunger or in the tube! While it sounds like it would lubricate it nicely in reality it causes it to seize up after a time.
Now that you have both components, it is now time to drill the holes. Pull the plunger out of the tube until it is an inch or so from the end. Then drill four holes in the pipe 1/2" below the bottom edge of the plunger in the direction of the stock assembly. These holes allow air to enter the tube without you having to pull the plunger all the way out of the tube.
Step 5: Test Fit and Cement
Make sure all the parts are moving correctly and then cement it together.
Don't cement the barrel onto the tee just yet.
Note: Don't sniff the glue fumes. It smells terrible!
Step 6: Use the Gun
The gun also works as a Nerf-dart launcher. Simply remove the barrel from the tee (I told you not to cement the barrel on for a reason!) and slip in the dart. Replace the barrel, pump the gun and shoot. To get good speed, you need to pump it about four times. With enough pumping, you can achieve frightening speeds!
It only works with the suction-cup type Nerf bullets.
If you make this, please post pictures!
I know there is room for improvement in this gun, so if you make any modifications or changes in design please tell me about it (and post pictures).
Thanks for looking!
And please, please, PLEASE don't shoot anyone's eye out! :-)