According to the Decibel X app it is 88 to 90db beside the rifle and back from the muzzle, which is about the sames as the DonnyFL .25/30 cal Shogun I have been shooting.
It is 88 to 89 db with the .22/25 air stripper and 89 to 90 db with the 25/30 air stripper
To be clear it is 10 degrees in ND today so I am shooting out my bedroom window, so probably not very accurate readings !
My M3 is .25 cal shooting NSA 33.6gr. slugs at 1000fps.
To my ear the Fat-Boy sounds slightly quieter than the Shogun.