You may not know this yet, but what you REALLY want is a pair of amplifying muffs that go behind your neck like these:
Peltor 6S
Now that I have been way too presumptuous, let me explain. I use these with the volume turned all the way up in conjunction with ear plugs. What that does is allow me to hear all the range commands and conversations (because they are amplified and make it through the ear plugs) but when a gun goes off, the amplification goes quiet and you get the benefits of being double plugged. While, in theory, serial attenuation like this should be completely additive, in practice it isn't completely serial (some of the sound pressure gets to your ears through your bones and connective tissue), so you really only get about 5dB of additional attenuation. Those 5 dB do make a huge difference, though.
Because of this imperfect serial attenuation, you probably won't see much difference between a 30 dB muff and a 19 dB muff IF YOU ARE DOUBLE PLUGGING.
BOTTOM LINE:
Your hearing will be safe shotgunning with only plugs if you install them correctly.
You will have a lot less noise if you double-plug
You will hear commands a LOT better if you double-plug with an amplifying muff like the one above.
Hope that helps,
Saands
ETA: After writing all that, I followed Robert's link above and it was to the same product ... I guess I have to say I agree!