This is my first air gun I have ever built.
I don't take any responsibility if some gets injured. This is at your own discretion. Anyway this is what you'll need:

Ball valve
Copper pipe( of your choice of diameter which is also your caliber)
Plastic bottle
Shrader valve ( bike valve)
And plumbers epoxy putty ( make sure it's plumbers epoxy putty, and not just regular plumbers putty other wise it won't work)

Tools:
hot glue gun with hot glue
Adjustable wrench
Drill with drill bits

Optional:

Wood ( for stock)
Hose clamps
Washer
And screw
Jigsaw
Sandpaper

I will also be making other instructables on this gun when I make it bolt action and maybe have a magazine. Also I might make a pressure chamber so it can be shot multiple times before being refilled with air.

Step 1: Get Your Materials and Begin

You have to have a copper pipe a bottle a ball valve and plumbers putty because these are the main components of your gun.

What you do is you put the copper pipe in the ball valve it's quite simple. Then you take your plastic bottle and drill a hole in the back. This is were you bike valve will go. You then take you plumbers epoxy putty and put it on the ball valve and bottle so it is a air tight seal. You can use hot glue on the bike valve but I recommend the epoxy putty. Follow the instructions on the package of the epoxy putty.

You are now done the basic version.

Just take a marble or make a paper cone and fill it with glue ram it down your copper pipe with the valve closed ( obviously) pump up the bottle to 40 psi you can go higher but for the first shot I recommend this. Now pull the valve handle quickly and it will shoot.

Step 2: Stock

You can make a stock out of wood, I just found a 2 by 6 and cut it out to the shape I wanted and then sanded it.

For the sights I took a screw and glued it to the front of the barrel. I then took a washer and glued it to the top of my wood frame.