Thanks for the Fort Collins report. Very well done. it is surprising that they found that double protection added up to 20 dB more. Most studies state that a 2nd level only adds 5 dB. I agree with you that most folks don't wear protection properly, and that at the range or in the field actual dB reduction is often far less than the rating of the plugs or muffs.F16jack, great summary. The only thing I would change is double protection can offer up to 50db of protection. There is a good test done by the Fort Collins police dept. https://www.cdc.gov/niosh/hhe/reports/pdfs/2002-0131-2898.pdf
the one thing not touched on yet, is that hearing protection varies greatly depending on how it worn. Tests show most people don’t wear it correctly and only get around 15db on average from foam ear plugs. This is with a plug that can test to 30+ when used correctly. I have verified this on myself with testing. Fully inserted 30+, pulled out 1/4” and protection drops significantly. Honestly a suppressor does so much more to protect our hearing it’s criminal that we can’t just go down to the store and buy one.