From the trigger being depressed through to the ear-splitting crack of a gunshot, (certainly more noticeable on a range however than in the bush) hearing loss is inescapable and for the ear, an irreparable problem.
From the moment the firing pin/ striker impacts the primer to the igniting powder sending the projectile on its journey up the bore there is a pressure wave forming in front of the projectile. This is known as the precursor wave or bow wave. This is created by the accelerating projectile displacing the air forward of the projectile in the bore.
As the pressure in the chamber intensifies, another pressure wave is being formed by the burning propellant. This pressure wave is gaining velocity at approximately 2-3 times faster than the terminal velocity of the projectile.
Once the projectile leaves the bore the high pressure gas behind the projectile, which is known as the blast wave is released.
It is the release of this wave that creates the ear-splitting sound of the gun shot, and it is the effect of this secondary pressure wave that moderators are designed to mitigate.