Yes, nice graphics, but the fact I was questioning was the resultant db level post doubled-up hearing protection as posted and quoted above:
OK, there you go. 3M says that wearing ear plugs under muffs only gives you an addition 5 decibels of protection:
https://multimedia.3m.com/mws/media/1527800O/earmuff-misconceptions.pdf
It doesn't give you and extra 30. Only five.
So if you wear a 30 ear muff with a NRR of 30, plus plugs, you are only reducing the sound reaching your ear by 35 decibles. (In reality, 3M says that to be safe, you should assume you are only being protected 1/2 as much as the NRR, due to imperfect use.)
View the chart below:
A .308 rifle produces 170 or so decibels.
If you wear muffs plus plugs correctly, that brings down the sound to your ear to about
135 decibles.
That is below the threshold of pain- but it is still WAY TOO LOUD. It will produce permeant hearing damage that you will not notice until it is too late. Don't believe me? Call up an audiologist and ask them!
If you add a suppressor, the total produced by the gun is about 149 decibels. Add plugs and a muff with perfect use, and it brings down the sound to your ear to about 114 decibels. Heck, even that is too loud, but still not nearly as damaging at 135.
(an increase in sound of 6 decibels roughly doubles the noise pressure).
Buy suppressors so you don't end up with hyperacusis and tinnitus like me.