Build a Multiple Shot Airgun

This article has been updated on 5-29-09 with new info!

More Than One Shot Per Fill! Method 1: Self Contained
One of the most frustrating things about many of my homemade airguns is the fact that it takes about a minute to fill and reload between each shot. Here is a crude model that illustrates one way that you can get more than one shot per fill:

How It Works
To make it get more than one shot per fill, I added a ball valve to separate the air chamber into 2 parts:

To fill, the ball valve is left open until the overall chamber pressure is 150 psi, or lower depending on the type of ammo I shoot. The ball valve is then closed, and I fill the remaining chamber space up to 250 psi. I take a shot, open the ballvalve a hair, allowing the air to slowly fill the firing chamber, and close it off again. This gives me another 150 psi shot. To get the third shot, open the ball valve a hair. Once the hissing stops, open it completely and you have a shot anywhere from 80 to 120 psi.

Safety
It is important that you only open the ball valve a hair. To do otherwise will overload the sprinkler valve, potentially firing a unintended shot if the gun were loaded.

Results
I've used this gun to shoot homemade darts. I shoot them at lower pressures, typically between 40 and 60 psi. At 60 psi, the dart will punch through 2" of pine, with about an inch of dart protruding. One of the benefits of shooting lower pressures is the quietness of the report. I've also shot 180 gr. muzzleloading ball ammo at 150 psi, getting 2 good shots per fill.

More Than One Shot Per Fill! Method 2:Remote Air Supply
By storing your air outside the airgun, you can get several more shots per fill. The basic idea is the same as above, just applied on a larger scale. Check out my video on how I got 8+ shots on a single fill:

Combine the airpack with this idea, possibly adding a solar panel, and you will have a self sufficient air supply. Or, you can carry a small air pump to do the same trick without the complexity of electricity.