So the first thing that I am going to get out of the way is this:

WARNING: Blowguns should not be pointed at people, animals, or any living thing. Projectiles shot at high velocity may cause deep wounds leading to infection, and/or may cause loss of vision if hit in the eye. They can also break glass, and cause damage to property. This project should only be attempted with adequate knowledge, training, and adult supervision. Use caution and common sense. Use of this content is at your own risk.

There, now that we got the boring part out of the way lets take a look at blowguns.

At the hardware store you can pick up a 2 foot length of 1/2” PVC pipe, and a reducing adapter. The female adapter is 3/4” on one side, and reduces to a 1/2” slip connector on the other.

If you simply push the adapter onto the tube and give it a little tap, you've just created a super simple blowgun that can be used right away.

You can see the weighted darts fly amazingly straight, and will take out paper cups with an impressive amount of power. They’re just strong enough to do a little damage, but still safe enough to shoot around the house. Not that you should. But you could.

There are quite a lot of steps in this process and you can find them all spelled out here  But before you go take a look at this video. It's crazy what a bit of PVC pipe and a few darts can do!

Source: Instructables.