My theory is that adrenaline shuts off the hearing circuit to protect it, but that may not be correct.
Your theory is not correct, and the technical term do describe what is happening is called auditory exclusion. Many times during self defense situations, and even hunting, many people don't remember hearing the shots. However, just because they didn't hear the shots does not mean they did not cause damage to their ears. Hearing loss is cumulative, just because you don't notice the damage right away does not mean damage has not occurred. Anytime you fire a gun, even a .22 pistol, without hearing protection you are causing damage to your ears however miniscule it may be.