Know how a nail gun works.
How Nails Are Released - When air pressure flows into the gun from the compressor, it is stored in a chamber until the plunger, located at the muzzle, is depressed and the trigger is pulled. A properly working nail gun will not fire until the plunger is pressed against the object you're nailing. When the plunger is depressed, the air pressure is allowed to flow through the chamber, above a piston that is attached to a blade. Located above the piston is another plunger. The compressed air forces the plunger up and allows the pressure access to the top of the piston.