That's somewhat inaccurate. The stapedius muscle as part of the auditory reflex (above 85 dB) contracts and protects the cochlea from transmission of high intensity sound--but its function is variable across the population and it's uncertain if it actually prevents hearing damage. I'm guessing it mitigates it...
With that said, my 357 SIG P229 was a really loud gun and I hated shooting it at an indoor range.
OK, so not all plastic guns are bad