You will wind up with acoustic trauma....
As a musician, and somebody who's played in bands since my teens ( gosh, must near 20 years now ) I can tell you that all you need is 1 set of ear plugs.
You use 1 set of plugs, to take the db's down to a safe level. If you layer your plugs, you will create extra pressure in your tympanic membrane..
This will teach you all you need to know about ear plugs, custom plugs.. etc, etc.. Its for rock musicians...
meh, it also applies to gun ranges.
http://hearnet.com/
I can tell you that, "I know a lot of deaf musicians." But I was pretty bright, and had custom made plugs early on... When shooting, I just wear muffs, because of the gun powder in the air, etc, etc.. That would really screw up your custom plugs.
However, I wouldn't layer hearing protection. Its not going to help you. You will seriously damage yourself, thinking you are being, "extra safe."