Step 4: Simple Airgun Theory of Operation
When the volume of a sealed container decreases, the pressure increases, according to Boyle's Law. We hav made a perfectly sealed container with our piston. When we rapidly decrease the volume in the chamber, the pressure will increase, thus becoming able to shoot a projectile.
The gun is composed of two handles. One handle is connected to the outer cylinder, while the other is attached to the piston. The two handles begin apart, and are then pushed together quickly to create an area of high pressure to force out the projectile. See the diagram below.