Step 2: How the bolt works
Stage 1: The bolt is at rest and a magazine of NERF darts is loaded into the blaster.
Stage 2: The trigger is pressed and the solenoid valve allows a burst of air to pass into the piston assembly
Stage 3: The piston slides forward chambering the NERF dart into the barrel. At the end of it's extension the hole through the center of the piston passes the end of the pin riding through it. This allows the air in the piston to exit the barrel and propel the projectile.
Stage 4: The spring in the piston can now return it to the open position, and is now ready to fire again.
Just look at the pictures, it's harder to describe it in words.