This is a project i am currently working on - spring powered BB/Dart gun. Requires Spring, Metal/PVC pipe (Whichever you feel more secure with, i chose metal), Metal barrel, I chose 4.5mm .77 barrel from an old airgun, spring, some cutting of wood, and dowwel. This is alot more powerful than other bb guns powered by combustion, bike pumps ect. so be carefull.
Step 1: Materials
Airgun Spring - Check your local airgun shop, or if your australian, find one.
Wooden circles, cut with a hole saw
Metal tubing, to fit your spring.
Endcap for the tubing
4.5mm copper, or any other metal tubing for barrel, 4.5mm is .177 for metal bb's or airgun darts, although if you wanted to fire plastic bb's you will need 6mm tubing i think.
I think thats it *thinking face*
Step 2: First step (not really step two)
See picture, you only cut into one side of the piping, dont go all the way through
Step 3: Step Two
Add your spring to the tube
Step 4: Step Three
Now, put a holesaw on your drill with 4mm drill bit in and whatever holesaw bit you need to fit your spring tube, it has to be able to move in there, if need be file it down a bit if you dont have the right drill bit.
Then, throught the hole in the middle, glue the 4mm dowweling in.
Screw a screw in the top of your circle, the slide the screw down your cutting in the springtube, therefore compressing the spring, and then twist to the side, locking in place, this is how you cock your gun.
Put this in your spring tube.
Step 5: Step 4
Now copy step three, but put a 4.5mm drill bit in your drill with a little larger holesaw bit, this shouldnt move in the spring tube. drill your circle out.
INstead of dowweling use 4.5mm (hollow!) copper/metal pipe do not block it off at all, this is your barrel
Glue the hole thing onto the other end of your tube, like an endcap. all done:)