Without knowing the caliber, let's take a 308 as an example to see what would happen to the 5 day old child..
A .308 rifle shot is extremely loud, typically producing a sound level of around 165-170 decibels (dB) at the muzzle. For comparison, human pain threshold for noise is around 120-130 dB, and sounds above 140 dB can cause immediate and permanent hearing damage. Newborn babies have particularly sensitive hearing, as their auditory systems are still developing, making them even more vulnerable to loud noises.
If a newborn were close to a .308 rifle when it was fired—say, within a few feet—the intense sound pressure would almost certainly cause severe and immediate damage to their hearing. This could include:
- Ruptured Eardrums: The sudden pressure wave could tear the delicate eardrum, leading to pain, bleeding, and hearing loss.
- Permanent Hearing Loss: The cochlea, the inner ear structure responsible for converting sound into nerve signals, could be irreversibly damaged by the blast, resulting in partial or complete deafness.
- Tinnitus: A persistent ringing or buzzing in the ears could develop, though this might be harder to detect in a newborn.
- Long-term Developmental Impact: Since hearing is critical for language development in infants, such damage could lead to delays in speech and cognitive growth.
The proximity matters greatly. Even at a distance of 10-20 feet, without ear protection, the sound (still well above 140 dB) would pose a serious risk. Up close, the effect would be catastrophic. For context, a jet engine at takeoff (around 140-150 dB) is considered dangerous, and a rifle shot is significantly louder.
In short, a .308 rifle shot near a newborn would likely cause immediate, severe, and permanent hearing damage, potentially leaving them deaf. This is why firearms should never be discharged anywhere near unprotected ears, especially those of infants.