I use Alvis MK4 plugs firing and it is simply excellent; - To .22, using it open cap, you do not hear a clapping - .22 Pistol, closed cap, same - In 9mm, cap closed, the noise is barely louder, so perfect for me. - The 357 Magnum: noise a bit much, but still a good protection. - At 45: perhaps limit, it should be possible to test the model above (Alvis MK5), but since I mainly takes the 9mm I'll stick with the MK4.
Open cap, you clearly hear the human voice of someone priximit. Closed cap, it is necessary that the person be right next or speaks louder than normal, but it's still possible.
Conclusion: excellent product for use in a shooting range.
