It costs about $15 to construct, and is very fun to mess around with.
It shoots at roughly 600fps+ at 120psi with a .12gram airsoft bb and the excact specifications of the airgun made in this instructable.
And I must state that ***IT IS NOT MY FAULT IF YOU OR OTHERS ARE HURT OR KILLED AS A RESULT OF THIS AIRGUN***
And a couple tips (pretty much follow them or you will die,no joke)
*Never pressurize it over 140psi, even though it says rated to 480psi on the side.
*Never look down the barrel, even when you dont think it is loaded or pressurized
*Never aim at anything you do not intend to destroy
*Do not use this in an airsoft war, this is meant to just be something to mess around with. It will penetrated human flesh.
*Give the pvc cement and epoxy a full 24 hours to dry, no less.
Make sure you understand all those tips before going to next page.
And if you dont understand how a piston valve works then this is a helpful link.
Step 1: Getting Parts
1x 1/4in ball valve(metal)
2x 3/4in to 1/2in bushings(metal)
2x 3/4in female adapter(pvc)
1x length of 3/4in pipe of the desired size(pvc)
1x 1/2in copper cap
1x 6mm brass or aluminum tube of the desired length(might not be avaiable at your hardware store, try a hobby shop)
2x 1/2in to 1/4in bushing(metal)
1x 1/4in NPT schrader valve
3x 1/4in close nipples(prefferabley brass over steel)
1x double syringe container of epoxy
whatever tape strikes your fancy
bike inner tube
And some tools that you most likely have but if you dont you need to get them.
A vice is helpful but not nesessary
A nail(or similar)
And that is it
If you dont have some of tools the project will be a lot more pricey.