I dont think it dampens the sound at all. The barrel runs all the way throught it. It is just a shroud. Buy extra mags for it you need them. I put a rail and red dot on mine. They are very quiet. A lot of cheap fun to shoot. I would like to try running some CCI Quiet 22 throught it. I think the decibels from it is down in the 68 range.
i went to the range today. shot the new ak and the MP5. The mp5 held great groups just a little to the right. i forgot to bring an allen wrench to adjust it lol it had two fail to chambers, but that is because i had my hand blocking the spring loader on the magazine