There has been some past threads on this topic here on the OB. One interesting fact was raised about the research that a noted Otologist/Neurologist in San Antonio, Texas did. He was an avid hunter and had hearing loss and resulting tinnitus from firearms.
To add credibility he is most noted for being instrumental in developing the cochlear implants.
His detailed research found that your ear canal changes in shape/size from day to day or more often due to the fact that it is made up of mostly cartilage. It will change depending on how hydrated you are... how much water is in your body at that time.
So a custom set of plugs only really fit correctly based upon the molding of your ear canal on that particular day. So the actual NRR rating of that custom plug can vary greatly giving false perceived protection changing daily.
He also did research and stressed that electronic protection, no matter how fast they activate, still let the full sound through to your ear.... albeit for only a nanosecond.... and that after lots of exposure can still cause hearing loss.
He also talks about the amount of sound that still travels to your inner ear through your mastoid bone no matter how much you close your ear canal up..... and the need for muffs that cover that bone up as much as possible.
That's why doubling up with both plugs and muffs does not give you double NRR rating protection as you would think.
Another real interesting fact he stated was to shoot with your moth closed as much as possible as high decibels can travel to the inner ear from your mouth/throat by both the eustacion tube and jaw structure if your mouth is open.
His end recommendation, for maximum hearing protection from unsuppressed firearms, was to wear large diameter ear muffs rated at 32-33NRR and correctly inserted foam ear plugs also rated at 32-33NRR at the same time. Key words " correctly inserted".
