But the ported barrel and the huge volume of the suppressor make it a benchmark IMHO. I really think this weapon firing Movie Blanks is louder than the real SD with 124Gr ammo. Like I said that is just my opinion but other than the Pssot and the bolt noise very quiet indeed.
I usually try to make it to Guncraft Sports in Knoxville once a month. Even though I don't visit very often, I'm almost gueranteed to have someone shooting C-3 close by, or be shooting it myself! There was an AWC Amphibian MK-II there recently. I had "light" ear plugs in, and couldn't hear anything but a VERY faint "snick" when the action cycled.... VERY cool . As for the MP-5SD, I've never heard one personally, but I hope to soon I've heard several muzzle cans, and in the rifle catagory, I must say that Gemtech's Vortex, on a bolt gun with subsonic ammo is very near silent... With all these as comparison, It's quite a challenge I'm up against to create a better mousetrap, or should I say gas trap ! I'm counting the days til' I can send in the forms!