A couple of quick points, from a guy who runs a hearing clinic...
NRR should be taken with a grain of salt. It is tested under ideal conditions, which are unlikely to be met in the field. NRR is useful in comparing products with one another, but not very useful in telling an individual how much actual noise reduction he will experience.
Custom molded earplugs do not generally offer superior noise reduction, but rather improved comfort. If a person is comfortable enough with proper fitting over-the-counter plugs, there is no real advantage to buying expensive custom plugs. (If you do see your audiologist for customs, make sure to ask for open-mouth impressions and a soft material for the plugs. This will help ensure a good seal). I have never had custom plugs which I felt were completely adequate against gunfire.
After studying it for the last twenty years or so, I believe we rarely are able to fully protect ourselves from gunfire. The exceptions, in my opinion, are A) subsonic .22 RF with properly fitted muffs or plugs, and B) suppressed weapons fired outdoors with both plugs and muffs in place. For those of us who are just "regular" shooters - i.e. rifles and handguns without suppressors, fired indoors or out, with muffs, plugs, or both - we most likely will suffer some degree of damage over the course of a lifetime of shooting.