One weekend, when I was really bored, I had an idea. "What if I made a gun to shoot mini marshmallows?" I decided that compressed air was the safest way to propel a 'shmallow, so I got plannin'. After a few trips to Home Depot, I had a primitive gun. The compressed air was created using a simple bicycle pump, and the pump had to remain connected to the gun in order for the air to stay in the chamber. After a bit more planning, I came up with a design that used an electric air compressor and another valve to keep the compressed air compressed. I also realized that the barrel I had was the perfect size for a marble...I bought a sack of marbles from the store, and started shooting em. I was amazed. At 70-80 psi, the marble shot 150-200 feet! It was the perfect ammunition. The compressed-air marble gun was born!
The construction of the gun is actually pretty simple. There is a chamber of large-diameter PVC to hold the air, which has a valve on each end. The rear valve (right) is to hold in the compressed air after it is in the chamber, while the front valve is used to release the air. Directly in front of the release valve is the barrel of the gun (below). A compressor is hooked up to the air needle stuck in the rubber stopper at the rear, and the gun is "inflated." The gun turned out to be a huge hit with friends and neighbors.