
The top picture is a simple way to create higher pressures in your chamber.
Air is pumped into the larger side, because of the greater area of the large piston, the smaller diameter chamber is at a much higher pressure.
The Bottom picture is a gun designed to achieve high velocities of small caliber rounds. (He later found out this idea is very similar to a light gas gun.)
A heavy piston (steel/lead filled plastic) Is fired using high pressure air. The piston is shot along the barrel. Before the piston reaches the the hole 9/10 of the way down the barrel, all the pressure built up escapes through the hole. When the piston (With very high kinetic energy) passes the hole, the pressure builds up rapidly and breaks the burst disk/O-ring seal, propelling the projectile out very high velocity.
Obviously the tubing past the hole will need to be able to withstand very high pressures and and a rubber bumper will be needed to remove any energy remaining.
Ask any question if you don't understand.
