You can get the best results by having foam earplugs in your ears and having a decent pair of electronic muffs on and volume up to max.
If you have Howard Leight Impact Sport muffs, you have the lowest level of decent, acceptable electronic muffs in my opinion. If they cost $50-$60 retail, they should be decent. Higher priced ones are better.
However, if you have Caldwell or Frankford Arsenal, $20-$30, they are junk and lack the circuitry to offer decent amplification. They will protect your hearing but they cut the audio for FAR too long a time and don't allow you to hear much.