My Vulcan .25 with the Petr mod and LDC is measuring 79-80dB at 45 degrees and 6 feet from the end of the barrel. Shooting a tuned velocity of 900fps. Gun was shooting 945fps as delivered and the noise is really about the same.
As a comparison the sound of cycling the action to chamber a round was registering at 68dB.
My hand clap was registering about 70dB at this same distance. Ambient noise was registering 30dB.