By the numbers, 7 doesn't sound like much. But based on experience and a bit of dabbling in sound testing at work, you have to understand that the NRR values are weighted, and based on a broad spectrum sound measurement. These play fair with everyone else by providing a NRR rating. From 20Hz to 20,000Hz, the overall reduction may only be 7, but in the range that matters as pertains to a muzzle blast, they work pretty darn good! I'm not playing favoritism... just think you might be surprised. I was.
Speaking of which...
Where can I find the standards and procedures for establishing the NPR rating?
I was trying to find some information last week, but couldn't find anything online.